Clear ui::Layer damaged_region_ after commit.

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 <memory>
 #include <utility>
 
@@ skipping 671 matching lines @@
 }
 
 void Layer::SendDamagedRects() {
   if (damaged_region_.IsEmpty())
     return;
   if (!delegate_ && !mailbox_.IsValid())
     return;
 
   for (cc::Region::Iterator iter(damaged_region_); iter.has_rect(); iter.next())
     cc_layer_->SetNeedsDisplayRect(iter.rect());
-}
 
-void Layer::ClearDamagedRects() {
+  paint_region_.Union(damaged_region_);

[danakj, 2016/05/31 19:53:15]

Do you think we should union only when it's a painting (picture) layer?

   damaged_region_.Clear();
 }
 
 void Layer::CompleteAllAnimations() {
   typedef std::vector<scoped_refptr<LayerAnimator> > LayerAnimatorVector;
   LayerAnimatorVector animators;
   CollectAnimators(&animators);
   for (LayerAnimatorVector::const_iterator it = animators.begin();
        it != animators.end();
        ++it) {
@@ skipping 44 matching lines @@
 
 gfx::Rect Layer::PaintableRegion() {
   return gfx::Rect(size());
 }
 
 scoped_refptr<cc::DisplayItemList> Layer::PaintContentsToDisplayList(
     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));
-  ClearDamagedRects();
+      gfx::IntersectRects(paint_region_.bounds(), local_bounds));
+  paint_region_.Clear();
   cc::DisplayItemListSettings settings;
   settings.use_cached_picture = false;
   scoped_refptr<cc::DisplayItemList> display_list =
       cc::DisplayItemList::Create(PaintableRegion(), settings);
   if (delegate_) {
     delegate_->OnPaintLayer(
         PaintContext(display_list.get(), device_scale_factor_, invalidation));
   }
   display_list->Finalize();
   return display_list;
@@ skipping 278 matching lines @@
   if (animator_) {
     animator_->ResetCompositor(compositor);
     animator_->RemoveFromCollection(collection);
   }
 
   for (auto* child : children_)
     child->ResetCompositorForAnimatorsInTree(compositor);
 }
 
 }  // namespace ui