Attempting to reland the Overview Button Change.

ash/shell_observer.h

Index: ash/shell_observer.h
diff --git a/ash/shell_observer.h b/ash/shell_observer.h
index c2b652cdf56e6928087d5b1dc6cc061d1225532f..d1b3d8651c258597e4a2f3f0459989b23a60e36e 100644
--- a/ash/shell_observer.h
+++ b/ash/shell_observer.h
@@ -47,6 +47,14 @@ class ASH_EXPORT ShellObserver {
   // to their final position).
   virtual void OnOverviewModeEnding() {}
 
+  // Called when the always maximize mode has started. Windows might still
+  // animate though.
+  virtual void OnMaximizeModeStarted() {}
+
+  // Called when the always maximize mode has ended. Windows may still be
+  // animating but have been restored.
+  virtual void OnMaximizeModeEnded() {}
+
  protected:
   virtual ~ShellObserver() {}
 };