[ash-md] Improves smoothness with many windows 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 250 matching lines @@
       original_transform_(window->GetTargetTransform()),
       original_opacity_(window->GetTargetOpacity()),
       weak_ptr_factory_(this) {}
 
 ScopedTransformOverviewWindow::~ScopedTransformOverviewWindow() {}
 
 void ScopedTransformOverviewWindow::RestoreWindow() {
   ScopedAnimationSettings animation_settings_list;
   BeginScopedAnimation(OverviewAnimationType::OVERVIEW_ANIMATION_RESTORE_WINDOW,
                        &animation_settings_list);
-  SetTransform(window()->GetRootWindow(), original_transform_, 0);
+  SetTransform(window()->GetRootWindow(), original_transform_, false, 0);
 
   std::unique_ptr<ScopedOverviewAnimationSettings> animation_settings =
       CreateScopedOverviewAnimationSettings(
           OverviewAnimationType::OVERVIEW_ANIMATION_LAY_OUT_SELECTOR_ITEMS,
           window_);
   gfx::Transform transform;
   if ((original_visibility_ == ORIGINALLY_MINIMIZED &&
        window_->GetShowState() != ui::SHOW_STATE_MINIMIZED) ||
       (original_visibility_ == ORIGINALLY_DOCKED_MINIMIZED &&
        window_->GetWindowState()->GetStateType() !=
@@ skipping 128 matching lines @@
   gfx::Transform transform;
   transform.Translate(dst_rect.x() - src_rect.x(), dst_rect.y() - src_rect.y());
   transform.Scale(static_cast<float>(dst_rect.width()) / src_rect.width(),
                   static_cast<float>(dst_rect.height()) / src_rect.height());
   return transform;
 }
 
 void ScopedTransformOverviewWindow::SetTransform(
     WmWindow* root_window,
     const gfx::Transform& transform,
+    bool use_masks,
     float radius) {
   DCHECK(overview_started_);
 
   if (ash::MaterialDesignController::IsOverviewMaterial() &&
       &transform != &original_transform_) {
-    if (!mask_) {
+    if (use_masks && !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);
-
+    if (mask_) {
+      mask_->layer()->SetBounds(bounds);
+      mask_->set_radius(radius);
+      window()->GetLayer()->SchedulePaint(bounds);
+    }
     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);
+        use_masks ? window()->GetIntProperty(WmWindowProperty::TOP_VIEW_INSET)
+                  : 0;
     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 42 matching lines @@
   if (parent_window)
     parent_window->CloseWidget();
 }
 
 // static
 void ScopedTransformOverviewWindow::SetImmediateCloseForTests() {
   immediate_close_for_tests = true;
 }
 
 }  // namespace ash