Add WorkspaceObserver to observe changes in workspace state

ui/aura_shell/workspace/workspace.cc

 // Copyright (c) 2011 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 "ui/aura_shell/workspace/workspace.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "ui/aura/aura_constants.h"
@@ skipping 162 matching lines @@
   }
   Layout(shift_reached_until ? until : NULL, NULL);
   return pushed;
 }
 
 void Workspace::Activate() {
   workspace_manager_->SetActiveWorkspace(this);
 }
 
 void Workspace::Layout(aura::Window* ignore, aura::Window* no_animation) {
+  workspace_manager_->set_layout_in_progress(true);
   gfx::Rect work_area = workspace_manager_->GetWorkAreaBounds(bounds_);
   int total_width = GetTotalWindowsWidth();
   if (total_width < work_area.width()) {
     int dx = (work_area.width() - total_width) / 2;
     for (aura::Window::Windows::iterator i = windows_.begin();
          i != windows_.end();
          ++i) {
       if (*i != ignore) {
         MoveWindowTo(*i,
                      gfx::Point(work_area.x() + dx, work_area.y()),
@@ skipping 10 matching lines @@
                    work_area.origin(),
                    no_animation != windows_[0]);
     }
     if (windows_.size() == 2 && windows_[1] != ignore) {
       MoveWindowTo(windows_[1],
                    gfx::Point(work_area.right() - GetLayoutWidth(windows_[1]),
                               work_area.y()),
                    no_animation != windows_[1]);
     }
   }
+  workspace_manager_->set_layout_in_progress(false);
 }
 
 bool Workspace::ContainsFullscreenWindow() const {
   for (aura::Window::Windows::const_iterator i = windows_.begin();
        i != windows_.end();
        ++i) {
     aura::Window* w = *i;
     if (w->IsVisible() &&
         w->GetIntProperty(aura::kShowStateKey) == ui::SHOW_STATE_FULLSCREEN)
       return true;
@@ skipping 46 matching lines @@
 
 // static
 size_t Workspace::SetMaxWindowsCount(size_t max) {
   int old = g_max_windows_per_workspace;
   g_max_windows_per_workspace = max;
   return old;
 }
 
 }  // namespace internal
 }  // namespace aura_shell