Bug 1576463 - canvas toDataURL and toBlob should not throw for serialization errors, r=jya

Differential Revision: https://phabricator.services.mozilla.com/D45121

--HG--
extra : moz-landing-system : lando

dom/base/ImageEncoder.cpp

@@ -106,6 +106,8 @@ class EncodingCompleteEvent : public CancelableRunnable {
       MOZ_ASSERT(blob);
 
       rv = callback->ReceiveBlob(blob.forget());
+    } else {
+      rv = callback->ReceiveBlob(nullptr);
     }
 
     return rv;

dom/canvas/CanvasRenderingContextHelper.cpp

@@ -35,10 +35,15 @@ void CanvasRenderingContextHelper::ToBlob(
     nsresult ReceiveBlob(already_AddRefed<Blob> aBlob) override {
       RefPtr<Blob> blob = aBlob;
 
-      RefPtr<Blob> newBlob = Blob::Create(mGlobal, blob->Impl());
+      RefPtr<Blob> newBlob;
+
+      if (blob) {
+        newBlob = Blob::Create(mGlobal, blob->Impl());
+      }
 
       RefPtr<BlobCallback> callback(mBlobCallback.forget());
       ErrorResult rv;
+
       callback->Call(newBlob, rv);
 
       mGlobal = nullptr;

dom/html/HTMLCanvasElement.cpp

@@ -603,7 +603,10 @@ void HTMLCanvasElement::ToDataURL(JSContext* aCx, const nsAString& aType,
     return;
   }
 
-  aRv = ToDataURLImpl(aCx, aSubjectPrincipal, aType, aParams, aDataURL);
+  nsresult rv = ToDataURLImpl(aCx, aSubjectPrincipal, aType, aParams, aDataURL);
+  if (NS_FAILED(rv)) {
+    aDataURL.AssignLiteral("data:,");
+  }
 }
 
 void HTMLCanvasElement::SetMozPrintCallback(PrintCallback* aCallback) {