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

ash/common/shelf/shelf_view.cc

Index: ash/common/shelf/shelf_view.cc
diff --git a/ash/common/shelf/shelf_view.cc b/ash/common/shelf/shelf_view.cc
index 65c6941072d06dfbf69652b98d8070a1ac9aafbb..9dfc0531bb82d854f0c3055deb6ed5333376a75c 100644
--- a/ash/common/shelf/shelf_view.cc
+++ b/ash/common/shelf/shelf_view.cc
@@ -754,9 +754,9 @@ void ShelfView::LayoutToIdealBounds() {
   overflow_button_->SetBoundsRect(ideal_bounds.overflow_bounds);
 }
 
-void ShelfView::UpdateShelfItemBackground(int alpha) {
-  GetAppListButton()->SetBackgroundAlpha(alpha);
-  overflow_button_->SetBackgroundAlpha(alpha);
+void ShelfView::UpdateShelfItemBackground(SkColor color) {
+  GetAppListButton()->UpdateShelfItemBackground(color);
+  overflow_button_->UpdateShelfItemBackground(color);
 }
 
 void ShelfView::UpdateAllButtonsVisibilityInOverflowMode() {