Add a FOUC painting test.

Source/platform/graphics/GraphicsLayer.cpp

Index: Source/platform/graphics/GraphicsLayer.cpp
diff --git a/Source/platform/graphics/GraphicsLayer.cpp b/Source/platform/graphics/GraphicsLayer.cpp
index 6c27628d2cea91ee20f22808ca0b84abb2ca9c98..e15babb6513ab10daf510749a693ff545fe281c1 100644
--- a/Source/platform/graphics/GraphicsLayer.cpp
+++ b/Source/platform/graphics/GraphicsLayer.cpp
@@ -460,6 +460,14 @@ void GraphicsLayer::resetTrackedPaintInvalidations()
     paintInvalidationTrackingMap().remove(this);
 }
 
+bool GraphicsLayer::hasTrackedPaintInvalidations() const
+{
+    PaintInvalidationTrackingMap::iterator it = paintInvalidationTrackingMap().find(this);
+    if (it != paintInvalidationTrackingMap().end())
+        return !it->value.invalidationRects.isEmpty();
+    return false;
+}
+
 void GraphicsLayer::trackPaintInvalidationRect(const FloatRect& rect)
 {
     if (rect.isEmpty())