Make the ChromeOS overview window clear its mask

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 382 matching lines @@
 
 void ScopedTransformOverviewWindow::SetTransform(
     WmWindow* root_window,
     const gfx::Transform& transform,
     int radius) {
   DCHECK(overview_started_);
 
   if (ash::MaterialDesignController::IsOverviewMaterial() && !mask_) {
     mask_.reset(new OverviewContentMask(
         window()->GetIntProperty(WmWindowProperty::TOP_VIEW_INSET), radius));
+    mask_->layer()->SetFillsBoundsOpaquely(false);

[varkha, 2016/07/09 11:26:13]

Brilliant, thanks for a quick tip!
The code here [1] has the same problem, right?
[1] -
https://cs.chromium.org/chromium/src/ui/views/bubble/tray_bubble_view.cc?q=Se...

     mask_->layer()->SetBounds(GetTargetBoundsInScreen());
     window()->GetLayer()->SetMaskLayer(mask_->layer());
   }
 
   gfx::Point target_origin(GetTargetBoundsInScreen().origin());
 
   for (auto* window : GetTransientTreeIterator(window_)) {
     WmWindow* parent_window = window->GetParent();
     gfx::Point original_origin =
         parent_window->ConvertRectToScreen(window->GetTargetBounds()).origin();
@@ skipping 35 matching lines @@
   if (parent_window)
     parent_window->CloseWidget();
 }
 
 // static
 void ScopedTransformOverviewWindow::SetImmediateCloseForTests() {
   immediate_close_for_tests = true;
 }
 
 }  // namespace ash