Add a FOUC painting test.

Source/platform/graphics/GraphicsLayer.h

Index: Source/platform/graphics/GraphicsLayer.h
diff --git a/Source/platform/graphics/GraphicsLayer.h b/Source/platform/graphics/GraphicsLayer.h
index 22dd3c4856bd6c8a005b0a862d7b6958c4642952..efb150fd7b219979c13275ea3ae087a0f7686052 100644
--- a/Source/platform/graphics/GraphicsLayer.h
+++ b/Source/platform/graphics/GraphicsLayer.h
@@ -220,6 +220,7 @@ public:
 
     bool isTrackingPaintInvalidations() const { return m_client->isTrackingPaintInvalidations(); }
     void resetTrackedPaintInvalidations();
+    bool hasTrackedPaintInvalidations() const;
     void trackPaintInvalidationRect(const FloatRect&);
     void trackPaintInvalidationObject(const String&);
 
@@ -252,6 +253,8 @@ public:
     // Exposed for tests.
     virtual WebLayer* contentsLayer() const { return m_contentsLayer; }
 
+    ContentLayerDelegate* contentLayerDelegateForTesting() const { return m_contentLayerDelegate.get(); }
+
 #ifndef NDEBUG
     DisplayItemClient displayItemClient() const { return toDisplayItemClient(this); }
     String debugName() const { return m_client->debugName(this) + " debug red fill"; }