2D canvas: fix shadow rendering with compositing modes that require temp layers

Source/platform/graphics/GraphicsTypes.h

Index: Source/platform/graphics/GraphicsTypes.h
diff --git a/Source/platform/graphics/GraphicsTypes.h b/Source/platform/graphics/GraphicsTypes.h
index 2fac7768d65d047ae35551759ea143da3c01d2bc..25f59421218926f315df9d2b79725ea2bf64525c 100644
--- a/Source/platform/graphics/GraphicsTypes.h
+++ b/Source/platform/graphics/GraphicsTypes.h
@@ -72,6 +72,12 @@ enum CompositeOperator {
     CompositeDifference
 };
 
+enum ShadowMode {
+    DrawShadowAndForeground,
+    DrawShadowOnly,
+    DrawForegroundOnly

[jbroman, 2014/10/14 21:09:48]

This doesn't sound like a shadow mode to me; why not just clear the shadow in
this case?

+};
+
 enum GradientSpreadMethod {
     SpreadMethodPad,
     SpreadMethodReflect,