4 files changed, 30 insertions, 3 deletions

diff --git a/ash/shell.cc b/ash/shell.cc
index d0cf6ec..f1a037b 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -382,6 +382,14 @@ void Shell::OnCastingSessionStartedOrStopped(bool started) {
 #endif
 }
 
+void Shell::OnOverviewModeStarting() {
+  FOR_EACH_OBSERVER(ShellObserver, observers_, OnOverviewModeStarting());
+}
+
+void Shell::OnOverviewModeEnding() {
+  FOR_EACH_OBSERVER(ShellObserver, observers_, OnOverviewModeEnding());
+}
+
 void Shell::CreateShelf() {
   RootWindowControllerList controllers = GetAllRootWindowControllers();
   for (RootWindowControllerList::iterator iter = controllers.begin();
diff --git a/ash/shell.h b/ash/shell.h
index 02aaef3..ae79a29 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -291,6 +291,14 @@ class ASH_EXPORT Shell
   // Called when a casting session is started or stopped.
   void OnCastingSessionStartedOrStopped(bool started);
 
+  // Called when the overview mode is about to be started (before the windows
+  // get re-arranged).
+  void OnOverviewModeStarting();
+
+  // Called before the overview mode is ending (before the windows get arranged
+  // to their final position).
+  void OnOverviewModeEnding();
+
   // Initializes |shelf_|.  Does nothing if it's already initialized.
   void CreateShelf();
 
diff --git a/ash/shell_observer.h b/ash/shell_observer.h
index 9d1db02..c2b652c 100644
--- a/ash/shell_observer.h
+++ b/ash/shell_observer.h
@@ -39,6 +39,14 @@ class ASH_EXPORT ShellObserver {
   virtual void OnFullscreenStateChanged(bool is_fullscreen,
                                         aura::Window* root_window) {}
 
+  // Called when the overview mode is about to be started (before the windows
+  // get re-arranged).
+  virtual void OnOverviewModeStarting() {}
+
+  // Called before the overview mode is ending (before the windows get arranged
+  // to their final position).
+  virtual void OnOverviewModeEnding() {}
+
  protected:
   virtual ~ShellObserver() {}
 };
diff --git a/ash/wm/overview/window_overview.cc b/ash/wm/overview/window_overview.cc
index 6bc5e56..f2a4b86 100644
--- a/ash/wm/overview/window_overview.cc
+++ b/ash/wm/overview/window_overview.cc
@@ -125,6 +125,8 @@ WindowOverview::WindowOverview(WindowSelector* window_selector,
       single_root_window_(single_root_window),
       overview_start_time_(base::Time::Now()),
       cursor_client_(NULL) {
+  Shell* shell = Shell::GetInstance();
+  shell->OnOverviewModeStarting();
   for (WindowSelectorItemList::iterator iter = windows_->begin();
        iter != windows_->end(); ++iter) {
     (*iter)->PrepareForOverview();
@@ -142,8 +144,7 @@ WindowOverview::WindowOverview(WindowSelector* window_selector,
     // as suggested there.
     cursor_client_->LockCursor();
   }
-  ash::Shell::GetInstance()->PrependPreTargetHandler(this);
-  Shell* shell = Shell::GetInstance();
+  shell->PrependPreTargetHandler(this);
   shell->metrics()->RecordUserMetricsAction(UMA_WINDOW_OVERVIEW);
   HideAndTrackNonOverviewWindows();
 }
@@ -163,10 +164,12 @@ WindowOverview::~WindowOverview() {
   }
   if (cursor_client_)
     cursor_client_->UnlockCursor();
-  ash::Shell::GetInstance()->RemovePreTargetHandler(this);
+  ash::Shell* shell = ash::Shell::GetInstance();
+  shell->RemovePreTargetHandler(this);
   UMA_HISTOGRAM_MEDIUM_TIMES(
       "Ash.WindowSelector.TimeInOverview",
       base::Time::Now() - overview_start_time_);
+  shell->OnOverviewModeEnding();
 }
 
 void WindowOverview::SetSelection(size_t index) {