cc: Use a ListContainer for DisplayItemList to reduce allocations.

cc/resources/display_item_list.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 CC_RESOURCES_DISPLAY_ITEM_LIST_H_
 #define CC_RESOURCES_DISPLAY_ITEM_LIST_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/trace_event/trace_event.h"
 #include "cc/base/cc_export.h"
 #include "cc/base/scoped_ptr_vector.h"
+// TODO(danakj): Move ListContainer out of cc/quads/
+#include "cc/quads/list_container.h"
 #include "cc/resources/display_item.h"
 #include "cc/resources/pixel_ref_map.h"
 #include "skia/ext/refptr.h"
 #include "third_party/skia/include/core/SkPicture.h"
 #include "ui/gfx/geometry/rect.h"
 
 class SkCanvas;
 class SkDrawPictureCallback;
 class SkPictureRecorder;
 
 namespace cc {
 
 class CC_EXPORT DisplayItemList
     : public base::RefCountedThreadSafe<DisplayItemList> {
  public:
   static scoped_refptr<DisplayItemList> Create(gfx::Rect layer_rect,
                                                bool use_cached_picture);
 
   void Raster(SkCanvas* canvas,
               SkDrawPictureCallback* callback,
               float contents_scale) const;
 
-  void AppendItem(scoped_ptr<DisplayItem> item);
+  template <typename DisplayItemType>
+  DisplayItemType* CreateAndAppendItem() {
+#if DCHECK_IS_ON()
+    needs_process_ = true;
+#endif
+    ProcessAppendedItemsOnTheFly();
+    return items_.AllocateAndConstruct<DisplayItemType>();
+  }
 
+  void ProcessAppendedItems();
   void CreateAndCacheSkPicture();
 
   bool IsSuitableForGpuRasterization() const;
   int ApproximateOpCount() const;
   size_t PictureMemoryUsage() const;
 
   scoped_refptr<base::trace_event::ConvertableToTraceFormat> AsValue() const;
 
   void EmitTraceSnapshot() const;
 
   void GatherPixelRefs(const gfx::Size& grid_cell_size);
 
  private:
   DisplayItemList(gfx::Rect layer_rect,
                   bool use_cached_picture,
                   bool retain_individual_display_items);
   DisplayItemList(gfx::Rect layer_rect, bool use_cached_picture);
   ~DisplayItemList();
-  ScopedPtrVector<DisplayItem> items_;
+
+  // While appending new items, if they are not being retained, this can process
+  // periodically to avoid retaining all the items and processing at the end.
+  void ProcessAppendedItemsOnTheFly();
+#if DCHECK_IS_ON()
+  bool ProcessAppendedItemsCalled() const { return !needs_process_; }
+  bool needs_process_;
+#else
+  bool ProcessAppendedItemsCalled() const { return true; }
+#endif
+
+  ListContainer<DisplayItem> items_;
   skia::RefPtr<SkPicture> picture_;
 
   scoped_ptr<SkPictureRecorder> recorder_;
   skia::RefPtr<SkCanvas> canvas_;
   bool use_cached_picture_;
   bool retain_individual_display_items_;
 
   gfx::Rect layer_rect_;
   bool is_suitable_for_gpu_rasterization_;
   int approximate_op_count_;
   size_t picture_memory_usage_;
 
   scoped_ptr<PixelRefMap> pixel_refs_;
 
   friend class base::RefCountedThreadSafe<DisplayItemList>;
   friend class PixelRefMap::Iterator;
   FRIEND_TEST_ALL_PREFIXES(DisplayItemListTest, PictureMemoryUsage);
   DISALLOW_COPY_AND_ASSIGN(DisplayItemList);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_DISPLAY_ITEM_LIST_H_