Blink-side contiguous allocation of display items.

Source/platform/graphics/paint/DisplayItem.h

Index: Source/platform/graphics/paint/DisplayItem.h
diff --git a/Source/platform/graphics/paint/DisplayItem.h b/Source/platform/graphics/paint/DisplayItem.h
index ed8985384fd6aee80bffa12ab56447a5271950e0..ecdbd12c3c65fa1a4a81c66d64f443f50529e16e 100644
--- a/Source/platform/graphics/paint/DisplayItem.h
+++ b/Source/platform/graphics/paint/DisplayItem.h
@@ -18,6 +18,7 @@
 
 namespace blink {
 
+class DisplayItems;
 class GraphicsContext;
 class WebDisplayItemList;
 
@@ -233,6 +234,7 @@ public:
     bool skippedCache() const { return m_skippedCache; }
 
     virtual void appendToWebDisplayItemList(WebDisplayItemList*) const { }
+    virtual void appendByMoving(DisplayItems&) = 0;
 
     // See comments of enum Type for usage of the following macros.
 #define DEFINE_CATEGORY_METHODS(Category) \
@@ -355,6 +357,27 @@ private:
     virtual bool isEnd() const override final { return true; }
 };
 
+// Allows a DisplayItemClientWrapper to be constructed from a DisplayItem, in
+// order to facilitate copying it.
+// TODO(jbroman): This is a bad class name.
+class DisplayItemClientWrapperHelper {

[Xianzhu, 2015/06/19 16:19:11]

I think we can just use DisplayItemClientWrapper if we rename
DisplayItem::clientDebugString() to debugName() and make it declared in both
debug and release build.

+    DISALLOW_ALLOCATION();
+public:
+    DisplayItemClientWrapperHelper(const DisplayItem& wrapped) : m_wrapped(wrapped) { }
+    DisplayItemClient displayItemClient() const { return m_wrapped.client(); }
+    String debugName() const
+    {
+#ifndef NDEBUG
+        return m_wrapped.clientDebugString();
+#else
+        return String();
+#endif
+    }
+private:
+    const DisplayItem& m_wrapped;
+};
+
+
 } // namespace blink
 
 #endif // DisplayItem_h