--- a/layout/style/ServoBindings.cpp
+++ b/layout/style/ServoBindings.cpp
@@ -1522,16 +1522,24 @@ Gecko_ImageValue_Create(ServoBundledURI 
   NS_ConvertUTF8toUTF16 url(reinterpret_cast<const char*>(aURI.mURLString),
                             aURI.mURLStringLength);
 
   RefPtr<css::ImageValue> value(
     new css::ImageValue(url, do_AddRef(aURI.mExtraData)));
   return value.forget().take();
 }
 
+MOZ_DEFINE_MALLOC_SIZE_OF(GeckoImageValueMallocSizeOf)
+
+size_t
+Gecko_ImageValue_SizeOfIncludingThis(mozilla::css::ImageValue* aImageValue)
+{
+  return aImageValue->SizeOfIncludingThis(GeckoImageValueMallocSizeOf);
+}
+
 void
 Gecko_SetLayerImageImageValue(nsStyleImage* aImage,
                               mozilla::css::ImageValue* aImageValue)
 {
   MOZ_ASSERT(aImage && aImageValue);
 
   RefPtr<nsStyleImageRequest> req =
     CreateStyleImageRequest(nsStyleImageRequest::Mode::Track, aImageValue);

--- a/layout/style/ServoBindings.h
+++ b/layout/style/ServoBindings.h
@@ -338,16 +338,17 @@ nsIAtom* Gecko_CounterStyle_GetName(cons
 const mozilla::AnonymousCounterStyle*
 Gecko_CounterStyle_GetAnonymous(const mozilla::CounterStylePtr* ptr);
 
 // background-image style.
 void Gecko_SetNullImageValue(nsStyleImage* image);
 void Gecko_SetGradientImageValue(nsStyleImage* image, nsStyleGradient* gradient);
 NS_DECL_THREADSAFE_FFI_REFCOUNTING(mozilla::css::ImageValue, ImageValue);
 mozilla::css::ImageValue* Gecko_ImageValue_Create(ServoBundledURI aURI);
+size_t Gecko_ImageValue_SizeOfIncludingThis(mozilla::css::ImageValue* aImageValue);
 void Gecko_SetLayerImageImageValue(nsStyleImage* image,
                                    mozilla::css::ImageValue* aImageValue);
 
 void Gecko_SetImageElement(nsStyleImage* image, nsIAtom* atom);
 void Gecko_CopyImageValueFrom(nsStyleImage* image, const nsStyleImage* other);
 void Gecko_InitializeImageCropRect(nsStyleImage* image);
 
 nsStyleGradient* Gecko_CreateGradient(uint8_t shape,

--- a/layout/style/nsCSSValue.cpp
+++ b/layout/style/nsCSSValue.cpp
@@ -2145,18 +2145,17 @@ nsCSSValue::SizeOfExcludingThis(mozilla:
 
     // URL
     case eCSSUnit_URL:
       n += mValue.mURL->SizeOfIncludingThis(aMallocSizeOf);
       break;
 
     // Image
     case eCSSUnit_Image:
-      // Not yet measured.  Measurement may be added later if DMD finds it
-      // worthwhile.
+      n += mValue.mImage->SizeOfIncludingThis(aMallocSizeOf);
       break;
 
     // Gradient
     case eCSSUnit_Gradient:
       n += mValue.mGradient->SizeOfIncludingThis(aMallocSizeOf);
       break;
 
     // TokenStream
@@ -3072,16 +3071,25 @@ css::ImageValue::~ImageValue()
       proxy->CancelAndForgetObserver(NS_BINDING_ABORTED);
     }
 
     iter.Remove();
   }
 }
 
 size_t
+css::ImageValue::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
+{
+  size_t n = aMallocSizeOf(this);
+  n += css::URLValueData::SizeOfExcludingThis(aMallocSizeOf);
+  n += mRequests.ShallowSizeOfExcludingThis(aMallocSizeOf);
+  return n;
+}
+
+size_t
 css::ComplexColorValue::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
 {
   // Only measure it if it's unshared, to avoid double-counting.
   size_t n = 0;
   if (mRefCnt <= 1) {
     n += aMallocSizeOf(this);
   }
   return n;

--- a/layout/style/nsCSSValue.h
+++ b/layout/style/nsCSSValue.h
@@ -214,17 +214,17 @@ struct ImageValue final : public URLValu
   ImageValue(const nsAString& aString,
              already_AddRefed<URLExtraData> aExtraData);
 
   ImageValue(const ImageValue&) = delete;
   ImageValue& operator=(const ImageValue&) = delete;
 
   void Initialize(nsIDocument* aDocument);
 
-  // XXXheycam We should have our own SizeOfIncludingThis method.
+  size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
 
 protected:
   ~ImageValue();
 
 public:
   // Inherit Equals from URLValueData
 
   nsRefPtrHashtable<nsPtrHashKey<nsIDocument>, imgRequestProxy> mRequests;