Remove layout during paint in Tab

chrome/browser/ui/views/tabs/tab.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/tabs/tab.h"
 
 #include <stddef.h>
 #include <limits>
 #include <utility>
 
@@ skipping 527 matching lines @@
   hover_controller_.SetAnimationContainer(container);
 }
 
 bool Tab::IsActive() const {
   return controller_->IsActiveTab(this);
 }
 
 void Tab::ActiveStateChanged() {
   OnButtonColorMaybeChanged();
   media_indicator_button_->UpdateEnabledForMuteToggle();
+
+  if (ShouldShowCloseBox() != showing_close_button_)

[miu, 2016/01/08 00:25:39]

I think we have to unconditionally call Layout() here.  The reason is that the
tab's active state changes the set of which buttons, favicon, title, etc. are
visible.

For reference, see the three methods starting here:
https://code.google.com/p/chromium/codesearch#chromium/src/chrome/browser/ui/...

Even if what you have here always results in the correct behavior, it implies
knowledge internal to c/b/ui/tabs/tab_utils.cc.

[enne (OOO), 2016/01/08 01:46:25]

Thanks! Updated the patch.

+    Layout();
 }
 
 bool Tab::IsSelected() const {
   return controller_->IsTabSelected(this);
 }
 
 void Tab::SetData(const TabRendererData& data) {
   DCHECK(GetWidget());
 
   if (data_.Equals(data))
@@ skipping 611 matching lines @@
   if (data().blocked == old.blocked)
     return;
 
   if (data().blocked)
     StartPulse();
   else
     StopPulse();
 }
 
 void Tab::PaintTab(gfx::Canvas* canvas) {
-  // See if the model changes whether the icons should be painted.
-  const bool show_icon = ShouldShowIcon();
-  const bool show_media_indicator = ShouldShowMediaIndicator();
-  const bool show_close_button = ShouldShowCloseBox();
-  if (show_icon != showing_icon_ ||
-      show_media_indicator != showing_media_indicator_ ||
-      show_close_button != showing_close_button_)
-    Layout();
-
   PaintTabBackground(canvas);
 
-  if (show_icon)
+  if (showing_icon_)
     PaintIcon(canvas);
 }
 
 void Tab::PaintImmersiveTab(gfx::Canvas* canvas) {
   // Use transparency for the draw-attention animation.
   int alpha = 255;
   if (pulse_animation_ && pulse_animation_->is_animating() && !data().pinned) {
     alpha = pulse_animation_->CurrentValueBetween(
         255, static_cast<int>(255 * kImmersiveTabMinThrobOpacity));
   }
@@ skipping 564 matching lines @@
                          const gfx::ImageSkia& image) {
   DCHECK_NE(scale_factor, ui::SCALE_FACTOR_NONE);
   ImageCacheEntry entry;
   entry.resource_id = resource_id;
   entry.scale_factor = scale_factor;
   entry.image = image;
   image_cache_->push_front(entry);
   if (image_cache_->size() > kMaxImageCacheSize)
     image_cache_->pop_back();
 }