Move overdraw tracking code from GraphicsContext to CanvasRenderingContext2D

Source/core/html/HTMLImageElement.cpp

Index: Source/core/html/HTMLImageElement.cpp
diff --git a/Source/core/html/HTMLImageElement.cpp b/Source/core/html/HTMLImageElement.cpp
index 0fba7de53c41faf22d9e383ef295d192dbb5840e..bcf7155b3064ba4f6290a8d8b5f7ba3968cac770 100644
--- a/Source/core/html/HTMLImageElement.cpp
+++ b/Source/core/html/HTMLImageElement.cpp
@@ -725,4 +725,11 @@ void HTMLImageElement::setUseFallbackContent()
     EventDispatchForbiddenScope::AllowUserAgentEvents allowEvents;
     ensureUserAgentShadowRoot();
 }
+
+bool HTMLImageElement::isOpaque() const
+{
+    Image* image = const_cast<HTMLImageElement*>(this)->imageContents();
+    return image && image->currentFrameKnownToBeOpaque();
+}
+
 }