Add initial implementation of cc::Surfaces backend for exo.

components/exo/shell_surface.cc

 // Copyright 2015 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 "components/exo/shell_surface.h"
 
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ash/wm/aura/wm_window_aura.h"
 #include "ash/wm/common/window_resizer.h"
@@ skipping 927 matching lines @@
     aura::Window::ConvertPointToTarget(widget_->GetNativeWindow(),
                                        widget_->GetNativeWindow()->parent(),
                                        &new_widget_origin);
     new_widget_bounds.set_origin(new_widget_origin);
   }
 
   // Set |ignore_window_bounds_changes_| as this change to window bounds
   // should not result in a configure request.
   DCHECK(!ignore_window_bounds_changes_);
   ignore_window_bounds_changes_ = true;
-  widget_->SetBounds(new_widget_bounds);
+  if (current_bounds_ != new_widget_bounds)

[reveman, 2016/05/27 23:30:45]

nit: would be nice to land this as a separate patch unless it's actually
specific the use of surface layers

+    widget_->SetBounds(new_widget_bounds);
+  current_bounds_ = new_widget_bounds;
   ignore_window_bounds_changes_ = false;
 
   UpdateTransparentInsets();
 
   // A change to the widget size requires surface bounds to be re-adjusted.
   surface_->SetBounds(gfx::Rect(GetSurfaceOrigin(), surface_->layer()->size()));
 }
 
 void ShellSurface::UpdateTransparentInsets() {
   DCHECK(widget_);
 
   gfx::Rect non_transparent_bounds = surface_->GetNonTransparentBounds() +
                                      GetSurfaceOrigin().OffsetFromOrigin();
   gfx::Size window_size = widget_->GetNativeWindow()->bounds().size();
   gfx::Insets transparent_insets =
       gfx::Rect(window_size).InsetsFrom(non_transparent_bounds);
   ash::wm::WindowState* window_state =
       ash::wm::GetWindowState(widget_->GetNativeWindow());
   if (window_state->transparent_insets() != transparent_insets) {
     window_state->set_transparent_insets(transparent_insets);
     ash::Shell::GetInstance()->UpdateShelfVisibility();
   }
 }
 
 }  // namespace exo