--- a/gfx/2d/2D.h
+++ b/gfx/2d/2D.h
@@ -932,17 +932,17 @@ public:
    * normally return the same SourceSurface object.
    */
   virtual already_AddRefed<SourceSurface> Snapshot() = 0;
 
   // Snapshots the contents and returns an alpha mask
   // based on the RGB values.
   virtual already_AddRefed<SourceSurface> IntoLuminanceSource(LuminanceType aLuminanceType,
                                                               float aOpacity);
-  virtual IntSize GetSize() = 0;
+  virtual IntSize GetSize() const = 0;
 
   /**
    * If possible returns the bits to this DrawTarget for direct manipulation. While
    * the bits is locked any modifications to this DrawTarget is forbidden.
    * Release takes the original data pointer for safety.
    */
   virtual bool LockBits(uint8_t** aData, IntSize* aSize,
                         int32_t* aStride, SurfaceFormat* aFormat,

--- a/gfx/2d/DrawTargetCairo.cpp
+++ b/gfx/2d/DrawTargetCairo.cpp
@@ -676,17 +676,17 @@ DrawTargetCairo::GetType() const
       MOZ_CRASH("GFX: Unsupported cairo surface type");
     }
   }
   MOZ_ASSERT(false, "Could not determine DrawTargetType for DrawTargetCairo");
   return DrawTargetType::SOFTWARE_RASTER;
 }
 
 IntSize
-DrawTargetCairo::GetSize()
+DrawTargetCairo::GetSize() const
 {
   return mSize;
 }
 
 SurfaceFormat
 GfxFormatForCairoSurface(cairo_surface_t* surface)
 {
   cairo_surface_type_t type = cairo_surface_get_type(surface);

--- a/gfx/2d/DrawTargetCairo.h
+++ b/gfx/2d/DrawTargetCairo.h
@@ -60,17 +60,17 @@ public:
 
   DrawTargetCairo();
   virtual ~DrawTargetCairo();
 
   virtual bool IsValid() const override;
   virtual DrawTargetType GetType() const override;
   virtual BackendType GetBackendType() const override { return BackendType::CAIRO; }
   virtual already_AddRefed<SourceSurface> Snapshot() override;
-  virtual IntSize GetSize() override;
+  virtual IntSize GetSize() const override;
 
   virtual bool IsCurrentGroupOpaque() override;
 
   virtual void SetPermitSubpixelAA(bool aPermitSubpixelAA) override;
 
   virtual bool LockBits(uint8_t** aData, IntSize* aSize,
                         int32_t* aStride, SurfaceFormat* aFormat,
                         IntPoint* aOrigin = nullptr) override;

--- a/gfx/2d/DrawTargetCapture.h
+++ b/gfx/2d/DrawTargetCapture.h
@@ -32,17 +32,17 @@ public:
   virtual BackendType GetBackendType() const override { return mRefDT->GetBackendType(); }
   virtual DrawTargetType GetType() const override { return mRefDT->GetType(); }
   virtual bool IsCaptureDT() const override { return true; }
   virtual already_AddRefed<SourceSurface> Snapshot() override;
   virtual already_AddRefed<SourceSurface> IntoLuminanceSource(LuminanceType aLuminanceType,
                                                               float aOpacity) override;
   virtual void SetPermitSubpixelAA(bool aPermitSubpixelAA) override;
   virtual void DetachAllSnapshots() override;
-  virtual IntSize GetSize() override { return mSize; }
+  virtual IntSize GetSize() const override { return mSize; }
   virtual void Flush() override {}
   virtual void DrawSurface(SourceSurface *aSurface,
                            const Rect &aDest,
                            const Rect &aSource,
                            const DrawSurfaceOptions &aSurfOptions,
                            const DrawOptions &aOptions) override;
   virtual void DrawFilter(FilterNode *aNode,
                           const Rect &aSourceRect,

--- a/gfx/2d/DrawTargetD2D1.h
+++ b/gfx/2d/DrawTargetD2D1.h
@@ -35,17 +35,17 @@ public:
   DrawTargetD2D1();
   virtual ~DrawTargetD2D1();
 
   virtual DrawTargetType GetType() const override { return DrawTargetType::HARDWARE_RASTER; }
   virtual BackendType GetBackendType() const override { return BackendType::DIRECT2D1_1; }
   virtual already_AddRefed<SourceSurface> Snapshot() override;
   virtual already_AddRefed<SourceSurface> IntoLuminanceSource(LuminanceType aLuminanceType,
                                                               float aOpacity) override;
-  virtual IntSize GetSize() override { return mSize; }
+  virtual IntSize GetSize() const override { return mSize; }
 
   virtual void Flush() override;
   virtual void DrawSurface(SourceSurface *aSurface,
                            const Rect &aDest,
                            const Rect &aSource,
                            const DrawSurfaceOptions &aSurfOptions,
                            const DrawOptions &aOptions) override;
   virtual void DrawFilter(FilterNode *aNode,

--- a/gfx/2d/DrawTargetDual.h
+++ b/gfx/2d/DrawTargetDual.h
@@ -44,17 +44,17 @@ public:
     mFormat = aA->GetFormat();
   }
      
   virtual DrawTargetType GetType() const override { return mA->GetType(); }
   virtual BackendType GetBackendType() const override { return mA->GetBackendType(); }
   virtual already_AddRefed<SourceSurface> Snapshot() override {
     return MakeAndAddRef<SourceSurfaceDual>(mA, mB);
   }
-  virtual IntSize GetSize() override { return mA->GetSize(); }
+  virtual IntSize GetSize() const override { return mA->GetSize(); }
 
   virtual void DetachAllSnapshots() override;
 
   FORWARD_FUNCTION(Flush)
   FORWARD_FUNCTION1(PushClip, const Path *, aPath)
   FORWARD_FUNCTION1(PushClipRect, const Rect &, aRect)
   FORWARD_FUNCTION(PopClip)
   FORWARD_FUNCTION(PopLayer)

--- a/gfx/2d/DrawTargetRecording.h
+++ b/gfx/2d/DrawTargetRecording.h
@@ -25,17 +25,17 @@ public:
   virtual BackendType GetBackendType() const override { return BackendType::RECORDING; }
   virtual bool IsRecording() const override { return true; }
 
   virtual already_AddRefed<SourceSurface> Snapshot() override;
   virtual already_AddRefed<SourceSurface> IntoLuminanceSource(LuminanceType aLuminanceType, float aOpacity) override;
 
   virtual void DetachAllSnapshots() override;
 
-  virtual IntSize GetSize() override { return mSize; }
+  virtual IntSize GetSize() const override { return mSize; }
 
   /* Ensure that the DrawTarget backend has flushed all drawing operations to
    * this draw target. This must be called before using the backing surface of
    * this draw target outside of GFX 2D code.
    */
   virtual void Flush() override { mFinalDT->Flush(); }
 
   /*

--- a/gfx/2d/DrawTargetSkia.h
+++ b/gfx/2d/DrawTargetSkia.h
@@ -32,17 +32,17 @@ class DrawTargetSkia : public DrawTarget
 public:
   MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(DrawTargetSkia, override)
   DrawTargetSkia();
   virtual ~DrawTargetSkia();
 
   virtual DrawTargetType GetType() const override;
   virtual BackendType GetBackendType() const override { return BackendType::SKIA; }
   virtual already_AddRefed<SourceSurface> Snapshot() override;
-  virtual IntSize GetSize() override { return mSize; }
+  virtual IntSize GetSize() const override { return mSize; };
   virtual bool LockBits(uint8_t** aData, IntSize* aSize,
                         int32_t* aStride, SurfaceFormat* aFormat,
                         IntPoint* aOrigin = nullptr) override;
   virtual void ReleaseBits(uint8_t* aData) override;
   virtual void Flush() override;
   virtual void DrawSurface(SourceSurface *aSurface,
                            const Rect &aDest,
                            const Rect &aSource,

--- a/gfx/2d/DrawTargetTiled.h
+++ b/gfx/2d/DrawTargetTiled.h
@@ -42,17 +42,17 @@ public:
 
   virtual bool IsTiledDrawTarget() const override { return true; }
 
   virtual bool IsCaptureDT() const override { return mTiles[0].mDrawTarget->IsCaptureDT(); }
   virtual DrawTargetType GetType() const override { return mTiles[0].mDrawTarget->GetType(); }
   virtual BackendType GetBackendType() const override { return mTiles[0].mDrawTarget->GetBackendType(); }
   virtual already_AddRefed<SourceSurface> Snapshot() override;
   virtual void DetachAllSnapshots() override;
-  virtual IntSize GetSize() override {
+  virtual IntSize GetSize() const override {
     MOZ_ASSERT(mRect.Width() > 0 && mRect.Height() > 0);
     return IntSize(mRect.XMost(), mRect.YMost());
   }
 
   virtual void Flush() override;
   virtual void DrawSurface(SourceSurface *aSurface,
                            const Rect &aDest,
                            const Rect &aSource,

--- a/gfx/2d/DrawTargetWrapAndRecord.h
+++ b/gfx/2d/DrawTargetWrapAndRecord.h
@@ -25,17 +25,17 @@ public:
   virtual BackendType GetBackendType() const override { return mFinalDT->GetBackendType(); }
   virtual bool IsRecording() const override { return true; }
 
   virtual already_AddRefed<SourceSurface> Snapshot() override;
   virtual already_AddRefed<SourceSurface> IntoLuminanceSource(LuminanceType aLuminanceType, float aOpacity) override;
 
   virtual void DetachAllSnapshots() override;
 
-  virtual IntSize GetSize() override { return mFinalDT->GetSize(); }
+  virtual IntSize GetSize() const override { return mFinalDT->GetSize(); }
 
   /* Ensure that the DrawTarget backend has flushed all drawing operations to
    * this draw target. This must be called before using the backing surface of
    * this draw target outside of GFX 2D code.
    */
   virtual void Flush() override { mFinalDT->Flush(); }
 
   /*

--- a/layout/generic/TextDrawTarget.h
+++ b/layout/generic/TextDrawTarget.h
@@ -347,17 +347,17 @@ public:
   }
 
   already_AddRefed<SourceSurface> IntoLuminanceSource(LuminanceType aLuminanceType,
                                                       float aOpacity) override {
     MOZ_CRASH("TextDrawTarget: Method shouldn't be called");
     return nullptr;
   }
 
-  IntSize GetSize() override {
+  IntSize GetSize() const override {
     MOZ_CRASH("TextDrawTarget: Method shouldn't be called");
     return IntSize(1, 1);
   }
 
   void Flush() override {
     MOZ_CRASH("TextDrawTarget: Method shouldn't be called");
   }