ui: Cache the output of View::OnPaint when the View isn't invalid.

ui/compositor/layer.cc

 // Copyright (c) 2012 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.
 
 #include "ui/compositor/layer.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
@@ skipping 732 matching lines @@
       sk_canvas, device_scale_factor_));
   if (delegate_)
     delegate_->OnPaintLayer(PaintContext(canvas.get(), clip));
 }
 
 void Layer::PaintContentsToDisplayList(
     cc::DisplayItemList* display_list,
     const gfx::Rect& clip,
     ContentLayerClient::PaintingControlSetting painting_control) {
   TRACE_EVENT1("ui", "Layer::PaintContentsToDisplayList", "name", name_);
+  gfx::Rect local_bounds(bounds().size());
+  gfx::Rect invalidation(
+      gfx::IntersectRects(damaged_region_.bounds(), local_bounds));
+  DCHECK(clip.Contains(invalidation));
   ClearDamagedRects();
   if (!delegate_)
     return;
-  // TODO(danakj): Save the invalidation on the layer and pass that down
-  // instead of the |clip| here. That will break everything until View
-  // early-outs emit cached display items instead of nothing.
-  gfx::Rect invalidation = clip;
-  DCHECK(clip.Contains(invalidation));
   delegate_->OnPaintLayer(
       PaintContext(display_list, device_scale_factor_, clip, invalidation));
 }
 
 bool Layer::FillsBoundsCompletely() const { return fills_bounds_completely_; }
 
 bool Layer::PrepareTextureMailbox(
     cc::TextureMailbox* mailbox,
     scoped_ptr<cc::SingleReleaseCallback>* release_callback,
     bool use_shared_memory) {
@@ skipping 315 matching lines @@
       children_.end(),
       std::bind2nd(std::mem_fun(&Layer::RemoveAnimatorsInTreeFromCollection),
                    collection));
 }
 
 bool Layer::IsAnimating() const {
   return animator_.get() && animator_->is_animating();
 }
 
 }  // namespace ui