cc: Don't perform image analysis if the DisplayItemList has no images.

cc/paint/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_PAINT_DISPLAY_ITEM_LIST_H_
 #define CC_PAINT_DISPLAY_ITEM_LIST_H_
 
 #include <stddef.h>
 
 #include <memory>
 #include <utility>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/trace_event/trace_event.h"
 #include "cc/base/contiguous_container.h"
 #include "cc/base/rtree.h"
 #include "cc/paint/discardable_image_map.h"
 #include "cc/paint/display_item.h"
+#include "cc/paint/drawing_display_item.h"
 #include "cc/paint/image_id.h"
 #include "cc/paint/paint_export.h"
 #include "third_party/skia/include/core/SkPicture.h"
 #include "ui/gfx/color_space.h"
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 
 class SkCanvas;
 
 namespace base {
@@ skipping 81 matching lines @@
     return AllocateAndConstruct<DisplayItemType>(std::forward<Args>(args)...);
   }
 
   template <typename DisplayItemType, typename... Args>
   const DisplayItemType& CreateAndAppendDrawingItem(
       const gfx::Rect& visual_rect,
       Args&&... args) {
     visual_rects_.push_back(visual_rect);
     GrowCurrentBeginItemVisualRect(visual_rect);
 
-    return AllocateAndConstruct<DisplayItemType>(std::forward<Args>(args)...);
+    const auto& item =
+        AllocateAndConstruct<DisplayItemType>(std::forward<Args>(args)...);
+    has_discardable_images_ |= item.picture->HasDiscardableImages();
+    return item;
   }
 
   // Called after all items are appended, to process the items and, if
   // applicable, create an internally cached SkPicture.
   void Finalize();
 
   void SetIsSuitableForGpuRasterization(bool is_suitable) {
     all_items_are_suitable_for_gpu_rasterization_ = is_suitable;
   }
   bool IsSuitableForGpuRasterization() const;
 
   int ApproximateOpCount() const;
   size_t ApproximateMemoryUsage() const;
   bool ShouldBeAnalyzedForSolidColor() const;
 
   void EmitTraceSnapshot() const;
 
-  void GenerateDiscardableImagesMetadata();
   void GetDiscardableImagesInRect(const gfx::Rect& rect,
                                   float contents_scale,
                                   const gfx::ColorSpace& target_color_space,
                                   std::vector<DrawImage>* images);
   gfx::Rect GetRectForImage(ImageId image_id) const;
 
   void SetRetainVisualRectsForTesting(bool retain) {
     retain_visual_rects_ = retain;
   }
 
   size_t size() const { return items_.size(); }
 
   gfx::Rect VisualRectForTesting(int index) { return visual_rects_[index]; }
 
   ContiguousContainer<DisplayItem>::const_iterator begin() const {
     return items_.begin();
   }
 
   ContiguousContainer<DisplayItem>::const_iterator end() const {
     return items_.end();
   }
 
+  bool has_discardable_images() const { return has_discardable_images_; }
+
  private:
   FRIEND_TEST_ALL_PREFIXES(DisplayItemListTest, AsValueWithNoItems);
   FRIEND_TEST_ALL_PREFIXES(DisplayItemListTest, AsValueWithItems);
 
   ~DisplayItemList();
 
   std::unique_ptr<base::trace_event::TracedValue> CreateTracedValue(
       bool include_items) const;
 
   // If we're currently within a paired display item block, unions the
   // given visual rect with the begin display item's visual rect.
   void GrowCurrentBeginItemVisualRect(const gfx::Rect& visual_rect);
 
   template <typename DisplayItemType, typename... Args>
   const DisplayItemType& AllocateAndConstruct(Args&&... args) {
     auto* item = &items_.AllocateAndConstruct<DisplayItemType>(
         std::forward<Args>(args)...);
     approximate_op_count_ += item->ApproximateOpCount();
     return *item;
   }
 
+  void GenerateDiscardableImagesMetadata();
+
   RTree rtree_;
   DiscardableImageMap image_map_;
   ContiguousContainer<DisplayItem> items_;
 
   // The visual rects associated with each of the display items in the
   // display item list. There is one rect per display item, and the
   // position in |visual_rects| matches the position of the item in
   // |items| . These rects are intentionally kept separate
   // because they are not needed while walking the |items| for raster.
   std::vector<gfx::Rect> visual_rects_;
   std::vector<size_t> begin_item_indices_;
 
   int approximate_op_count_ = 0;
   bool all_items_are_suitable_for_gpu_rasterization_ = true;
   // For testing purposes only. Whether to keep visual rects across calls to
   // Finalize().
   bool retain_visual_rects_ = false;
+  bool has_discardable_images_ = false;
 
   friend class base::RefCountedThreadSafe<DisplayItemList>;
   FRIEND_TEST_ALL_PREFIXES(DisplayItemListTest, ApproximateMemoryUsage);
   DISALLOW_COPY_AND_ASSIGN(DisplayItemList);
 };
 
 }  // namespace cc
 
 #endif  // CC_PAINT_DISPLAY_ITEM_LIST_H_