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

third_party/WebKit/Source/platform/graphics/paint/PaintController.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 PaintController_h
 #define PaintController_h
 
 #include "platform/PlatformExport.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/geometry/IntRect.h"
@@ skipping 90 matching lines @@
     // appends the cached display item to the new display list and returns true. Otherwise returns false.
     bool useCachedDrawingIfPossible(const DisplayItemClient&, DisplayItem::Type);
 
     // Tries to find the cached subsequence corresponding to the given parameters. If found, copies the
     // cache subsequence to the new display list and returns true. Otherwise returns false.
     bool useCachedSubsequenceIfPossible(const DisplayItemClient&);
 
     // True if the last display item is a begin that doesn't draw content.
     bool lastDisplayItemIsNoopBegin() const;
     void removeLastDisplayItem();
+    const DisplayItem* lastDisplayItem(unsigned offset);

[wkorman, 2016/07/26 18:41:08]

Perhaps worth documenting the lifespan of the item, add DCHECK/docs.

 
     void beginSkippingCache() { ++m_skippingCacheCount; }
     void endSkippingCache() { DCHECK(m_skippingCacheCount > 0); --m_skippingCacheCount; }
     bool isSkippingCache() const { return m_skippingCacheCount; }
 
     // Must be called when a painting is finished.
     // offsetFromLayoutObject is the offset between the space of the GraphicsLayer which owns this
     // PaintController and the coordinate space of the owning LayoutObject.
     void commitNewDisplayItems(const LayoutSize& offsetFromLayoutObject = LayoutSize());
 
@@ skipping 155 matching lines @@
 
 #if CHECK_DISPLAY_ITEM_CLIENT_ALIVENESS
     // A stack recording subsequence clients that are currently painting.
     Vector<const DisplayItemClient*> m_currentSubsequenceClients;
 #endif
 };
 
 } // namespace blink
 
 #endif // PaintController_h