[ash-md] Fixes a bug with setting window shape to mask header in overview

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 230 matching lines @@
   // Redrawing will take care of scale factor change.
 }
 
 base::Closure ScopedTransformOverviewWindow::OverviewContentMask::
     PrepareForLayerBoundsChange() {
   return base::Closure();
 }
 
 ScopedTransformOverviewWindow::ScopedTransformOverviewWindow(WmWindow* window)
     : window_(window),
+      determined_original_window_shape_(false),
       minimized_(window->GetShowState() == ui::SHOW_STATE_MINIMIZED),
       ignored_by_shelf_(window->GetWindowState()->ignored_by_shelf()),
       overview_started_(false),
       original_transform_(window->GetTargetTransform()),
       original_opacity_(window->GetTargetOpacity()),
       weak_ptr_factory_(this) {}
 
 ScopedTransformOverviewWindow::~ScopedTransformOverviewWindow() {}
 
 void ScopedTransformOverviewWindow::RestoreWindow() {
@@ skipping 148 matching lines @@
     if (!mask_) {
       mask_.reset(new OverviewContentMask(radius));
       mask_->layer()->SetFillsBoundsOpaquely(false);
       window()->GetLayer()->SetMaskLayer(mask_->layer());
     }
     gfx::Rect bounds(GetTargetBoundsInScreen().size());
     mask_->layer()->SetBounds(bounds);
     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));
+    if (!determined_original_window_shape_) {
+      determined_original_window_shape_ = true;
+      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));
       if (original_window_shape_)
         region->op(*original_window_shape_, SkRegion::kIntersect_Op);
       window()->GetLayer()->SetAlphaShape(base::WrapUnique(region));
       window()->SetMasksToBounds(true);
@@ skipping 44 matching lines @@
   if (parent_window)
     parent_window->CloseWidget();
 }
 
 // static
 void ScopedTransformOverviewWindow::SetImmediateCloseForTests() {
   immediate_close_for_tests = true;
 }
 
 }  // namespace ash