[ash-md] Doesn't recreate a rounded rect mask for overview windows

ash/common/wm/overview/scoped_transform_overview_window.cc

 // Copyright 2013 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 "ash/common/wm/overview/scoped_transform_overview_window.h"
 
 #include <algorithm>
 #include <vector>
 
 #include "ash/common/material_design/material_design_controller.h"
@@ skipping 165 matching lines @@
 }  // namespace
 
 // Mask layer that clips the window's original header in overview mode.
 // Only used with Material Design.
 class ScopedTransformOverviewWindow::OverviewContentMask
     : public ui::LayerDelegate {
  public:
   explicit OverviewContentMask(float radius);
   ~OverviewContentMask() override;
 
+  void set_radius(float radius) { radius_ = radius; }
   ui::Layer* layer() { return &layer_; }
 
   // Overridden from LayerDelegate.
   void OnPaintLayer(const ui::PaintContext& context) override;
   void OnDelegatedFrameDamage(const gfx::Rect& damage_rect_in_dip) override {}
   void OnDeviceScaleFactorChanged(float device_scale_factor) override;
   base::Closure PrepareForLayerBoundsChange() override;
 
  private:
   ui::Layer layer_;
@@ skipping 202 matching lines @@
 }
 
 void ScopedTransformOverviewWindow::SetTransform(
     WmWindow* root_window,
     const gfx::Transform& transform,
     float radius) {
   DCHECK(overview_started_);
 
   if (ash::MaterialDesignController::IsOverviewMaterial() &&
       &transform != &original_transform_) {
+    if (!mask_) {
+      mask_.reset(new OverviewContentMask(radius));
+      mask_->layer()->SetFillsBoundsOpaquely(false);
+      window()->GetLayer()->SetMaskLayer(mask_->layer());
+    }
     gfx::Rect bounds(GetTargetBoundsInScreen().size());
-    mask_.reset(new OverviewContentMask(radius));
-    mask_->layer()->SetFillsBoundsOpaquely(false);
     mask_->layer()->SetBounds(bounds);
-    window()->GetLayer()->SetMaskLayer(mask_->layer());
+    mask_->set_radius(radius);
+    window()->GetLayer()->SchedulePaint(bounds);
 
     SkRegion* window_shape = window()->GetLayer()->alpha_shape();
     if (!original_window_shape_ && window_shape)
       original_window_shape_.reset(new SkRegion(*window_shape));
     const int inset =
         window()->GetIntProperty(WmWindowProperty::TOP_VIEW_INSET);
     if (inset > 0) {
       bounds.Inset(0, inset, 0, 0);
       SkRegion* region = new SkRegion;
       region->setRect(RectToSkIRect(bounds));
@@ skipping 48 matching lines @@
   if (parent_window)
     parent_window->CloseWidget();
 }
 
 // static
 void ScopedTransformOverviewWindow::SetImmediateCloseForTests() {
   immediate_close_for_tests = true;
 }
 
 }  // namespace ash