[ash-md] Wired in the Shelf color to be derived from the Wallpaper.

ash/common/shelf/shelf_background_animator_observer.h

Index: ash/common/shelf/shelf_background_animator_observer.h
diff --git a/ash/common/shelf/shelf_background_animator_observer.h b/ash/common/shelf/shelf_background_animator_observer.h
index a2a021d69ce198e51070aaa7a35be6733dd4cc42..bf8ca1050f8b0071f8f6ddeeeacee913b8292ec3 100644
--- a/ash/common/shelf/shelf_background_animator_observer.h
+++ b/ash/common/shelf/shelf_background_animator_observer.h
@@ -6,6 +6,7 @@
 #define ASH_COMMON_SHELF_SHELF_BACKGROUND_ANIMATOR_OBSERVER_H_
 
 #include "ash/ash_export.h"
+#include "third_party/skia/include/core/SkColor.h"
 
 namespace ash {
 
@@ -13,10 +14,10 @@ namespace ash {
 class ASH_EXPORT ShelfBackgroundAnimatorObserver {
  public:
   // Called when the Shelf's background should be updated.
-  virtual void UpdateShelfBackground(int alpha) {}
+  virtual void UpdateShelfBackground(SkColor color) {}
 
   // Called when the Shelf item (aka button) backgrounds should be updated.
-  virtual void UpdateShelfItemBackground(int alpha) {}
+  virtual void UpdateShelfItemBackground(SkColor color) {}
 
  protected:
   virtual ~ShelfBackgroundAnimatorObserver() {}