Fold compositing display items into contained drawings if the drawing is a singleton.

third_party/WebKit/Source/platform/graphics/paint/DisplayItem.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 DisplayItem_h
 #define DisplayItem_h
 
 #include "platform/PlatformExport.h"
 #include "platform/graphics/ContiguousContainer.h"
 #include "platform/graphics/paint/DisplayItemClient.h"
@@ skipping 298 matching lines @@
     }
 #endif
 
     // True if the client is non-null. Because m_client is const, this should
     // never be false except when we explicitly create a tombstone/"dead display
     // item" as part of moving an item from one list to another (see:
     // DisplayItemList::appendByMoving).
     bool hasValidClient() const { return m_client; }
 
     virtual bool drawsContent() const { return false; }
+    virtual bool isBeginCompositingDisplayItem() const { return false; }

[Xianzhu, 2016/07/27 17:22:29]

You can avoid this virtual function by using "displayItem.type() ==
BeginCompositing" instead at the call site.

 
     // Override to implement specific analysis strategies.
     virtual void analyzeForGpuRasterization(SkPictureGpuAnalyzer&) const { }
 
 #ifndef NDEBUG
     static WTF::String typeAsDebugString(DisplayItem::Type);
     const WTF::String clientDebugString() const { return m_clientDebugString; }
     void setClientDebugString(const WTF::String& s) { m_clientDebugString = s; }
     WTF::String asDebugString() const;
     virtual void dumpPropertiesAsDebugString(WTF::StringBuilder&) const;
@@ skipping 49 matching lines @@
     bool isEndAndPairedWith(DisplayItem::Type otherType) const override = 0;
 #endif
 
 private:
     bool isEnd() const final { return true; }
 };
 
 } // namespace blink
 
 #endif // DisplayItem_h