Fixed the ScreenOrientationController so that it doesn't crash by animating

ash/rotator/screen_rotation_animator.h

 // 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.
 
 #ifndef ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_
 #define ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 #include "ui/gfx/display.h"
 
 namespace ash {
 
 // Utility to perform a screen rotation with an animation.
 class ASH_EXPORT ScreenRotationAnimator {
  public:
   explicit ScreenRotationAnimator(int64 display_id);
   ~ScreenRotationAnimator();
 
-  // Rotates |display_| to the |new_rotation| orientation.
+  // Returns true if the screen rotation animation can be completed
+  // successfully. For example an animation is not possible if |display_id_|
+  // specifies a gfx::Display that is not currently active. See
+  // www.crbug.com/479503.
+  bool CanAnimate() const;
+
+  // Rotates the gfx::Display specified by |display_id_| to the |new_rotation|
+  // orientation. Clients should only call |Rotate(gfx::Display::Rotation)| if
+  // |CanAnimate()| returns true.
   void Rotate(gfx::Display::Rotation new_rotation);
 
  private:
   // The id of the display to rotate.
   int64 display_id_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenRotationAnimator);
 };
 
 }  // namespace ash
 
 #endif  // ASH_ROTATOR_SCREEN_ROTATION_ANIMATOR_H_