--- a/dom/media/eme/CDMProxy.h
+++ b/dom/media/eme/CDMProxy.h
@@ -170,17 +170,17 @@ public:
 
   // Main thread only.
   virtual void OnResolveLoadSessionPromise(uint32_t aPromiseId,
                                            bool aSuccess) = 0;
 
   // Main thread only.
   virtual void OnSessionMessage(const nsAString& aSessionId,
                                 dom::MediaKeyMessageType aMessageType,
-                                nsTArray<uint8_t>& aMessage) = 0;
+                                const nsTArray<uint8_t>& aMessage) = 0;
 
   // Main thread only.
   virtual void OnExpirationChange(const nsAString& aSessionId,
                                   UnixTime aExpiryTime) = 0;
 
   // Main thread only.
   virtual void OnSessionClosed(const nsAString& aSessionId) = 0;
 

--- a/dom/media/eme/mediadrm/MediaDrmCDMProxy.cpp
+++ b/dom/media/eme/mediadrm/MediaDrmCDMProxy.cpp
@@ -221,17 +221,17 @@ MediaDrmCDMProxy::OnResolveLoadSessionPr
     return;
   }
   mKeys->OnSessionLoaded(aPromiseId, aSuccess);
 }
 
 void
 MediaDrmCDMProxy::OnSessionMessage(const nsAString& aSessionId,
                                    dom::MediaKeyMessageType aMessageType,
-                                   nsTArray<uint8_t>& aMessage)
+                                   const nsTArray<uint8_t>& aMessage)
 {
   MOZ_ASSERT(NS_IsMainThread());
   if (mKeys.IsNull()) {
     return;
   }
   RefPtr<dom::MediaKeySession> session(mKeys->GetSession(aSessionId));
   if (session) {
     session->DispatchKeyMessage(aMessageType, aMessage);

--- a/dom/media/eme/mediadrm/MediaDrmCDMProxy.h
+++ b/dom/media/eme/mediadrm/MediaDrmCDMProxy.h
@@ -72,17 +72,17 @@ public:
 
   void OnSetSessionId(uint32_t aCreateSessionToken,
                       const nsAString& aSessionId) override;
 
   void OnResolveLoadSessionPromise(uint32_t aPromiseId, bool aSuccess) override;
 
   void OnSessionMessage(const nsAString& aSessionId,
                         dom::MediaKeyMessageType aMessageType,
-                        nsTArray<uint8_t>& aMessage) override;
+                        const nsTArray<uint8_t>& aMessage) override;
 
   void OnExpirationChange(const nsAString& aSessionId,
                           UnixTime aExpiryTime) override;
 
   void OnSessionClosed(const nsAString& aSessionId) override;
 
   void OnSessionError(const nsAString& aSessionId,
                       nsresult aException,

--- a/dom/media/gmp/ChromiumCDMProxy.h
+++ b/dom/media/gmp/ChromiumCDMProxy.h
@@ -63,17 +63,17 @@ public:
 
   void OnSetSessionId(uint32_t aCreateSessionToken,
                       const nsAString& aSessionId) override;
 
   void OnResolveLoadSessionPromise(uint32_t aPromiseId, bool aSuccess) override;
 
   void OnSessionMessage(const nsAString& aSessionId,
                         dom::MediaKeyMessageType aMessageType,
-                        nsTArray<uint8_t>& aMessage) override;
+                        const nsTArray<uint8_t>& aMessage) override;
 
   void OnExpirationChange(const nsAString& aSessionId,
                           GMPTimestamp aExpiryTime) override;
 
   void OnSessionClosed(const nsAString& aSessionId) override;
 
   void OnSessionError(const nsAString& aSessionId,
                       nsresult aException,