arc: Implement proper Arc window activation for task moving to front.

components/exo/shell_surface.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 COMPONENTS_EXO_SHELL_SURFACE_H_
 #define COMPONENTS_EXO_SHELL_SURFACE_H_
 
 #include <deque>
 #include <memory>
 #include <string>
@@ skipping 79 matching lines @@
 
   // When the client is asked to configure the surface, it should acknowledge
   // the configure request sometime before the commit. |serial| is the serial
   // from the configure callback.
   void AcknowledgeConfigure(uint32_t serial);
 
   // Set the "parent" of this surface. This window should be stacked above a
   // parent.
   void SetParent(ShellSurface* parent);
 
+  // Activates the shell surface.
+  void Activate();
+
   // Maximizes the shell surface.
   void Maximize();
 
   // Minimize the shell surface.
   void Minimize();
 
   // Restore the shell surface.
   void Restore();
 
   // Set fullscreen state for shell surface.
@@ skipping 186 matching lines @@
   int top_inset_height_ = 0;
   int pending_top_inset_height_ = 0;
   float rectangular_shadow_background_opacity_ = 1.0;
 
   DISALLOW_COPY_AND_ASSIGN(ShellSurface);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_SHELL_SURFACE_H_