Implement DisplayList GatherPixelRefs

cc/resources/display_item_list.cc

Index: cc/resources/display_item_list.cc
diff --git a/cc/resources/display_item_list.cc b/cc/resources/display_item_list.cc
index f8ffbfd184b719d447447b35d58a867ec42d3940..b09111b82ba73c409928b8a2813df508358e2ae8 100644
--- a/cc/resources/display_item_list.cc
+++ b/cc/resources/display_item_list.cc
@@ -143,4 +143,13 @@ void DisplayItemList::EmitTraceSnapshot() const {
       "cc::DisplayItemList", this, AsValue());
 }
 
+void DisplayItemList::GatherPixelRefs(const gfx::Size& grid_cell_size) {
+  DCHECK(picture_);
+  pixel_refs_ = make_scoped_ptr(new PixelRefMap(grid_cell_size));
+  DCHECK(pixel_refs_->empty());

[vmpstr, 2015/03/31 17:10:31]

I don't think this is too useful, since you just created a new one in the line
above :)

If we expect this to be called only once however (I think that's the case), then
maybe DCHECK(!pixel_refs_) before you allocate though?

+  if (!picture_->willPlayBackBitmaps())
+    return;
+
+  pixel_refs_->GatherPixelRefsFromPicture(picture_.get());
+}
 }  // namespace cc