Reduce overdraw on bookmark bar

chrome/browser/ui/views/bookmarks/bookmark_bar_view.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 "chrome/browser/ui/views/bookmarks/bookmark_bar_view.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <limits>
@@ skipping 583 matching lines @@
       browser_(browser),
       browser_view_(browser_view),
       infobar_visible_(false),
       size_animation_(this),
       throbbing_view_(nullptr),
       bookmark_bar_state_(BookmarkBar::SHOW),
       animating_detached_(false),
       show_folder_method_factory_(this) {
   set_id(VIEW_ID_BOOKMARK_BAR);
   Init();
-
-  // Don't let the bookmarks show on top of the location bar while animating.
-  SetPaintToLayer();
-  layer()->SetMasksToBounds(true);
-  layer()->SetFillsBoundsOpaquely(false);
-
   size_animation_.Reset(1);
 }
 
 BookmarkBarView::~BookmarkBarView() {
   if (model_)
     model_->RemoveObserver(this);
 
   // It's possible for the menu to outlive us, reset the observer to make sure
   // it doesn't have a reference to us.
   if (bookmark_menu_) {
@@ skipping 26 matching lines @@
     bookmark_menu_->SetPageNavigator(navigator);
   if (context_menu_.get())
     context_menu_->SetPageNavigator(navigator);
 }
 
 void BookmarkBarView::SetBookmarkBarState(
     BookmarkBar::State state,
     BookmarkBar::AnimateChangeType animate_type) {
   if (animate_type == BookmarkBar::ANIMATE_STATE_CHANGE &&
       animations_enabled) {
+    if (!layer()) {
+      SetPaintToLayer();
+      layer()->SetMasksToBounds(true);
+      layer()->SetFillsBoundsOpaquely(false);
+    }
     animating_detached_ = (state == BookmarkBar::DETACHED ||
                            bookmark_bar_state_ == BookmarkBar::DETACHED);
     if (state == BookmarkBar::SHOW)
       size_animation_.Show();
     else
       size_animation_.Hide();
+    if (layer())
+      DestroyLayer();

[Evan Stade, 2017/05/24 17:34:30]

I am surprised this works. You're destroying the layer almost as soon as it's
being created. I would have thought you'd need to wait until AnimationEnded to
destroy the layer.

(also, I think it's safe to call DestroyLayer even if you don't have a layer.)

[sky, 2017/05/24 21:32:05]

I think it would be better to key off whether any descendant views have layers.
You can do this via OnChildLayerChanged(). I'm suggesting any time that function
is called you check if any visible descendants have layers. If they don't, then
the bookmarkbar shouldn't need a layer.

   } else {
     size_animation_.Reset(state == BookmarkBar::SHOW ? 1 : 0);
   }
   bookmark_bar_state_ = state;
 }
 
 const BookmarkNode* BookmarkBarView::GetNodeForButtonAtModelIndex(
     const gfx::Point& loc,
     int* model_start_index) {
   *model_start_index = 0;
@@ skipping 1493 matching lines @@
     return;
   apps_page_shortcut_->SetVisible(visible);
   UpdateBookmarksSeparatorVisibility();
   LayoutAndPaint();
 }
 
 void BookmarkBarView::OnShowManagedBookmarksPrefChanged() {
   if (UpdateOtherAndManagedButtonsVisibility())
     LayoutAndPaint();
 }