Implement Asynchronous image encoding for Canvas.toBlob

Source/core/html/HTMLCanvasElement.h

Index: Source/core/html/HTMLCanvasElement.h
diff --git a/Source/core/html/HTMLCanvasElement.h b/Source/core/html/HTMLCanvasElement.h
index 7173957a4058858e351c7dfdc0b3cc0cc92042ce..bc1ef5bdef10cab1d8587648402187540215071c 100644
--- a/Source/core/html/HTMLCanvasElement.h
+++ b/Source/core/html/HTMLCanvasElement.h
@@ -31,6 +31,7 @@
 #include "bindings/core/v8/ScriptValue.h"
 #include "bindings/core/v8/UnionTypesCore.h"
 #include "core/CoreExport.h"
+#include "core/dom/DOMTypedArray.h"
 #include "core/dom/Document.h"
 #include "core/dom/DocumentVisibilityObserver.h"
 #include "core/fileapi/FileCallback.h"
@@ -42,6 +43,7 @@
 #include "platform/graphics/GraphicsTypes3D.h"
 #include "platform/graphics/ImageBufferClient.h"
 #include "platform/heap/Handle.h"
+#include "public/platform/WebThread.h"
 
 #define CanvasDefaultInterpolationQuality InterpolationLow
 
@@ -114,7 +116,7 @@ public:
     String toDataURL(const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&) const;
     String toDataURL(const String& mimeType, ExceptionState& exceptionState) const { return toDataURL(mimeType, ScriptValue(), exceptionState); }
 
-    void toBlob(FileCallback*, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&) const;
+    void toBlob(FileCallback*, const String& mimeType, const ScriptValue& qualityArgument, ExceptionState&);
     void toBlob(FileCallback* callback, const String& mimeType, ExceptionState& exceptionState) { return toBlob(callback, mimeType, ScriptValue(), exceptionState); }
 
     // Used for rendering
@@ -209,7 +211,10 @@ private:
     bool paintsIntoCanvasBuffer() const;
 
     ImageData* toImageData(SourceDrawingBuffer) const;
-    String toDataURLInternal(const String& mimeType, const double* quality, SourceDrawingBuffer) const;
+    String toDataURLInternal(const String& mimeType, const double& quality, SourceDrawingBuffer) const;
+
+    void encodeImageAsync(DOMUint8ClampedArray* imagedata, IntSize imageSize, FileCallback*, const String& mimeType, double quality);
+    void createBlobAndCall(PassOwnPtr<Vector<char>> encodedImage, const String& mimeType, FileCallback*);
 
     WillBeHeapHashSet<RawPtrWillBeWeakMember<CanvasObserver>> m_observers;