Add WindowTreeHostPlatform::GetHost for Android build

ui/aura/window_tree_host_platform.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 UI_AURA_WINDOW_TREE_HOST_PLATFORM_H_
 #define UI_AURA_WINDOW_TREE_HOST_PLATFORM_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/aura/aura_export.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/platform_window/platform_window.h"
 #include "ui/platform_window/platform_window_delegate.h"
 
 namespace aura {
 
 // The unified WindowTreeHost implementation for platforms
 // that implement PlatformWindow.
 class AURA_EXPORT WindowTreeHostPlatform
     : public WindowTreeHost,
       public NON_EXPORTED_BASE(ui::PlatformWindowDelegate) {
  public:
   explicit WindowTreeHostPlatform(const gfx::Rect& bounds);
   ~WindowTreeHostPlatform() override;
 
+#if defined(OS_ANDROID)
+  // Returns the WindowTreeHostPlatform instance.
+  static WindowTreeHostPlatform* GetHost();
+#endif
+
   // WindowTreeHost:
   ui::EventSource* GetEventSource() override;
   gfx::AcceleratedWidget GetAcceleratedWidget() override;
   void ShowImpl() override;
   void HideImpl() override;
   gfx::Rect GetBounds() const override;
   void SetBounds(const gfx::Rect& bounds) override;
   gfx::Point GetLocationOnNativeScreen() const override;
   void SetCapture() override;
   void ReleaseCapture() override;
@@ skipping 23 matching lines @@
   gfx::NativeCursor current_cursor_;
   bool has_capture_;
   gfx::Rect bounds_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHostPlatform);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_TREE_HOST_PLATFORM_H_