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 269212ccc5b115d5429ecefb9fb545503bda123c..41660e4e7be70074d11a7919335b7105d95b46bc 100644
--- a/Source/core/html/HTMLImageElement.cpp
+++ b/Source/core/html/HTMLImageElement.cpp
@@ -723,4 +723,11 @@ void HTMLImageElement::setUseFallbackContent()
         return;
     ensureUserAgentShadowRoot();
 }
+
+bool HTMLImageElement::isOpaque() const
+{
+    Image* image = const_cast<HTMLImageElement*>(this)->imageContents();
+    return image && image->currentFrameKnownToBeOpaque();
+}
+
 }