Reland of "Apply Shelf/Dock opacity animations for the Material Design style."

ash/common/shelf/app_list_button.cc

Index: ash/common/shelf/app_list_button.cc
diff --git a/ash/common/shelf/app_list_button.cc b/ash/common/shelf/app_list_button.cc
index 7781625be42f4dcf1ec8efdc890ac578b2477da5..e31acdf85f0f02fcbe47d827aef833cfd177de0e 100644
--- a/ash/common/shelf/app_list_button.cc
+++ b/ash/common/shelf/app_list_button.cc
@@ -35,6 +35,7 @@ AppListButton::AppListButton(InkDropButtonListener* listener,
                              WmShelf* wm_shelf)
     : views::ImageButton(nullptr),
       draw_background_as_active_(false),
+      background_alpha_(0),
       listener_(listener),
       shelf_view_(shelf_view),
       wm_shelf_(wm_shelf) {
@@ -73,6 +74,11 @@ void AppListButton::OnAppListDismissed() {
     SchedulePaint();
 }
 
+void AppListButton::SetBackgroundAlpha(int alpha) {
+  background_alpha_ = alpha;
+  SchedulePaint();
+}
+
 bool AppListButton::OnMousePressed(const ui::MouseEvent& event) {
   ImageButton::OnMousePressed(event);
   shelf_view_->PointerPressedOnButton(this, ShelfView::MOUSE, event);
@@ -157,22 +163,16 @@ void AppListButton::OnPaint(gfx::Canvas* canvas) {
 }
 
 void AppListButton::PaintBackgroundMD(gfx::Canvas* canvas) {
-  SkPaint background_paint;
-  background_paint.setColor(SK_ColorTRANSPARENT);
-  background_paint.setFlags(SkPaint::kAntiAlias_Flag);
-  background_paint.setStyle(SkPaint::kFill_Style);
-
-  if (wm_shelf_->GetBackgroundType() ==
-      ShelfBackgroundType::SHELF_BACKGROUND_DEFAULT) {
-    background_paint.setColor(
-        SkColorSetA(kShelfBaseColor, GetShelfConstant(SHELF_BACKGROUND_ALPHA)));
-  }
-
   // Paint the circular background of AppList button.
   gfx::Point circle_center = GetContentsBounds().CenterPoint();
   if (!IsHorizontalAlignment(wm_shelf_->GetAlignment()))
     circle_center = gfx::Point(circle_center.y(), circle_center.x());
 
+  SkPaint background_paint;
+  background_paint.setColor(SkColorSetA(kShelfBaseColor, background_alpha_));
+  background_paint.setFlags(SkPaint::kAntiAlias_Flag);
+  background_paint.setStyle(SkPaint::kFill_Style);
+
   canvas->DrawCircle(circle_center, kAppListButtonRadius, background_paint);
 }