Implement Asynchronous image encoding for Canvas.toBlob

Source/platform/graphics/ImageBuffer.h

Index: Source/platform/graphics/ImageBuffer.h
diff --git a/Source/platform/graphics/ImageBuffer.h b/Source/platform/graphics/ImageBuffer.h
index 5d32e199a080e46cc3a8a1745fca83a1ab0ea524..46ccddbede4a7cc85eb1782d710a87e7191eddaa 100644
--- a/Source/platform/graphics/ImageBuffer.h
+++ b/Source/platform/graphics/ImageBuffer.h
@@ -153,8 +153,8 @@ private:
 
 struct ImageDataBuffer {
     ImageDataBuffer(const IntSize& size, const unsigned char* data) : m_data(data), m_size(size) { }
-    String PLATFORM_EXPORT toDataURL(const String& mimeType, const double* quality) const;
-    bool PLATFORM_EXPORT encodeImage(const String& mimeType, const double* quality, Vector<char>* output) const;
+    String PLATFORM_EXPORT toDataURL(const String& mimeType, const double& quality) const;
+    bool PLATFORM_EXPORT encodeImage(const String& mimeType, const double& quality, Vector<char>* output) const;
     const unsigned char* pixels() const { return m_data; }
     int height() const { return m_size.height(); }
     int width() const { return m_size.width(); }