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

ash/common/system/tray/tray_background_view.cc

Index: ash/common/system/tray/tray_background_view.cc
diff --git a/ash/common/system/tray/tray_background_view.cc b/ash/common/system/tray/tray_background_view.cc
index 569e939369e26c480a368488596996bd1150bdf7..3e26c5069993d2872ef9ae0d0f4602002b223bb3 100644
--- a/ash/common/system/tray/tray_background_view.cc
+++ b/ash/common/system/tray/tray_background_view.cc
@@ -89,26 +89,19 @@ class TrayBackground : public views::Background {
   const static int kNumOrientations = 2;
 
   explicit TrayBackground(TrayBackgroundView* tray_background_view)
-      : tray_background_view_(tray_background_view) {}
+      : tray_background_view_(tray_background_view), alpha_(0) {}
 
   ~TrayBackground() override {}
 
+  void set_alpha(int alpha) { alpha_ = alpha; }
+
  private:
   WmShelf* GetShelf() const { return tray_background_view_->shelf(); }
 
   void PaintMaterial(gfx::Canvas* canvas, views::View* view) const {
-    SkColor background_color = SK_ColorTRANSPARENT;
-    if (GetShelf()->GetBackgroundType() ==
-        ShelfBackgroundType::SHELF_BACKGROUND_DEFAULT) {
-      background_color = SkColorSetA(kShelfBaseColor,
-                                     GetShelfConstant(SHELF_BACKGROUND_ALPHA));
-    }
-
-    // TODO(bruthig|tdanderson): The background should be changed using a
-    // fade in/out animation.
     SkPaint background_paint;
     background_paint.setFlags(SkPaint::kAntiAlias_Flag);
-    background_paint.setColor(background_color);
+    background_paint.setColor(SkColorSetA(kShelfBaseColor, alpha_));
     canvas->DrawRoundRect(view->GetLocalBounds(), kTrayRoundedBorderRadius,
                           background_paint);
 
@@ -165,6 +158,8 @@ class TrayBackground : public views::Background {
   // Reference to the TrayBackgroundView for which this is a background.
   TrayBackgroundView* tray_background_view_;
 
+  int alpha_;
+
   DISALLOW_COPY_AND_ASSIGN(TrayBackground);
 };
 
@@ -359,13 +354,6 @@ void TrayBackgroundView::OnGestureEvent(ui::GestureEvent* event) {
   ActionableView::OnGestureEvent(event);
 }
 
-void TrayBackgroundView::UpdateBackground(int alpha) {
-  // The animator should never fire when the alternate shelf layout is used.
-  if (!background_ || draw_background_as_active_)
-    return;
-  SchedulePaint();
-}
-
 void TrayBackgroundView::SetContents(views::View* contents) {
   SetLayoutManager(new views::BoxLayout(views::BoxLayout::kVertical, 0, 0, 0));
   AddChildView(contents);
@@ -510,4 +498,11 @@ void TrayBackgroundView::UpdateBubbleViewArrow(
   // Nothing to do here.
 }
 
+void TrayBackgroundView::UpdateShelfItemBackground(int alpha) {
+  if (background_) {
+    background_->set_alpha(alpha);
+    SchedulePaint();
+  }
+}
+
 }  // namespace ash