Add a FOUC painting test.

public/platform/WebDisplayItemList.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WebDisplayItemList_h
 #define WebDisplayItemList_h
 
 #include "WebBlendMode.h"
 #include "WebFloatPoint.h"
 #include "WebFloatRect.h"
@@ skipping 16 matching lines @@
 
 // An ordered list of items representing content to be rendered (stored in
 // 'drawing' items) and operations to be performed when rendering this content
 // (stored in 'clip', 'transform', 'filter', etc...). For more details see:
 // http://dev.chromium.org/blink/slimming-paint.
 class WebDisplayItemList {
 public:
     virtual ~WebDisplayItemList() { }
 
     // This grabs a ref on the passed-in SkPicture.
-    virtual void appendDrawingItem(const SkPicture*) = 0;
+    virtual void appendDrawingItem(const SkPicture*) { }
 
-    virtual void appendClipItem(const WebRect&, const WebVector<SkRRect>&) = 0;
-    virtual void appendEndClipItem() = 0;
-    virtual void appendClipPathItem(const SkPath&, SkRegion::Op, bool antialias) = 0;
-    virtual void appendEndClipPathItem() = 0;
-    virtual void appendFloatClipItem(const WebFloatRect&) = 0;
-    virtual void appendEndFloatClipItem() = 0;
-    virtual void appendTransformItem(const SkMatrix44&) = 0;
-    virtual void appendEndTransformItem() = 0;
+    virtual void appendClipItem(const WebRect&, const WebVector<SkRRect>&) { }
+    virtual void appendEndClipItem() { }
+    virtual void appendClipPathItem(const SkPath&, SkRegion::Op, bool antialias) { }
+    virtual void appendEndClipPathItem() { }
+    virtual void appendFloatClipItem(const WebFloatRect&) { }
+    virtual void appendEndFloatClipItem() { }
+    virtual void appendTransformItem(const SkMatrix44&) { }
+    virtual void appendEndTransformItem() { }
     virtual void appendCompositingItem(float opacity,
-        SkXfermode::Mode, SkRect* bounds, SkColorFilter*) = 0;
-    virtual void appendEndCompositingItem() = 0;
+        SkXfermode::Mode, SkRect* bounds, SkColorFilter*) { }
+    virtual void appendEndCompositingItem() { }
 
-    virtual void appendFilterItem(const WebFilterOperations&, const WebFloatRect& bounds) = 0;
-    virtual void appendEndFilterItem() = 0;
+    virtual void appendFilterItem(const WebFilterOperations&, const WebFloatRect& bounds) { }
+    virtual void appendEndFilterItem() { }
 
     // Scroll containers are identified by an opaque pointer.
     using ScrollContainerId = const void*;
-    virtual void appendScrollItem(const WebSize& scrollOffset, ScrollContainerId) = 0;
-    virtual void appendEndScrollItem() = 0;
+    virtual void appendScrollItem(const WebSize& scrollOffset, ScrollContainerId) { }
+    virtual void appendEndScrollItem() { }
 };
 
 } // namespace blink
 
 #endif // WebDisplayItemList_h