CrOS Shelf: enable bg blur only when app list blue is on

Enable shelf background blur only when the launcher's background
blur is enabled.

This allows for a more consistent user experience, and may also
help with performance on some devices.

Bug: 879962,881134
Change-Id: I40015199f3312b62ef7b175167b65d5a9a6e352a
Reviewed-on: https://chromium-review.googlesource.com/1217584
Commit-Queue: Manu Cornet <manucornet@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590230}

ash/shelf/shelf_layout_manager.h

@@ -145,6 +145,9 @@ class ASH_EXPORT ShelfLayoutManager
   // it's only allowed in tablet mode, not in laptop mode.
   bool IsDraggingWindowFromTopOrCaptionArea() const;
 
+  // Returns whether background blur is enabled.
+  bool IsBackgroundBlurEnabled() { return is_background_blur_enabled_; }
+
   // Overridden from wm::WmSnapToPixelLayoutManager:
   void OnWindowResized() override;
   void SetChildBounds(aura::Window* child,

ash/shelf/shelf_widget.cc

@@ -217,7 +217,8 @@ void ShelfWidget::DelegateView::UpdateOpaqueBackground() {
         mask_ = views::Painter::CreatePaintedLayer(
             views::Painter::CreateSolidRoundRectPainter(SK_ColorBLACK, radius));
         mask_->layer()->SetBounds(opaque_background_bounds);
-        opaque_background_.SetBackgroundBlur(kShelfBlurRadius);
+        if (shelf_widget_->shelf_layout_manager()->IsBackgroundBlurEnabled())
+          opaque_background_.SetBackgroundBlur(kShelfBlurRadius);
         opaque_background_.SetMaskLayer(mask_->layer());
       }
     }
@@ -249,6 +250,7 @@ ShelfWidget::ShelfWidget(aura::Window* shelf_container, Shelf* shelf)
       background_animator_(SHELF_BACKGROUND_DEFAULT,
                            shelf_,
                            Shell::Get()->wallpaper_controller()),
+      shelf_layout_manager_(new ShelfLayoutManager(this, shelf)),
       delegate_view_(new DelegateView(this)),
       shelf_view_(new ShelfView(Shell::Get()->shelf_model(), shelf_, this)),
       login_shelf_view_(
@@ -279,7 +281,6 @@ ShelfWidget::ShelfWidget(aura::Window* shelf_container, Shelf* shelf)
   GetContentsView()->AddChildView(shelf_view_);
   GetContentsView()->AddChildView(login_shelf_view_);
 
-  shelf_layout_manager_ = new ShelfLayoutManager(this, shelf_);
   shelf_layout_manager_->AddObserver(this);
   shelf_container->SetLayoutManager(shelf_layout_manager_);
   background_animator_.PaintBackground(