Ensure that pinch-zoom scrollbar animations trigger a draw

cc/trees/layer_tree_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/animation/animation.h"
 #include "cc/animation/animation_id_provider.h"
 #include "cc/animation/keyframed_animation_curve.h"
@@ skipping 619 matching lines @@
   controller->AddAnimation(MakePinchZoomFadeAnimation(start_opacity,
     PinchZoomScrollbar::kDefaultOpacity));
 }
 
 void LayerTreeImpl::FadeInPinchZoomScrollbars() {
   if (!HasPinchZoomScrollbars() || page_scale_factor_ == 1)
     return;
 
   StartFadeInAnimation(PinchZoomScrollbarHorizontal());
   StartFadeInAnimation(PinchZoomScrollbarVertical());
+  SetNeedsRedraw();
 }
 
 static void StartFadeOutAnimation(LayerImpl* layer) {
   float opacity = layer->opacity();
   if (!opacity)
     return;
 
   LayerAnimationController* controller = layer->layer_animation_controller();
   // TODO(wjmaclean) It shouldn't be necessary to manually remove the old
   // animation.
   if (Animation* animation = controller->GetAnimation(Animation::Opacity))
     controller->RemoveAnimation(animation->id());
   controller->AddAnimation(MakePinchZoomFadeAnimation(opacity, 0));
 }
 
 void LayerTreeImpl::FadeOutPinchZoomScrollbars() {
   if (!HasPinchZoomScrollbars())
     return;
 
   StartFadeOutAnimation(PinchZoomScrollbarHorizontal());
   StartFadeOutAnimation(PinchZoomScrollbarVertical());
+  SetNeedsRedraw();
 }
 
 bool LayerTreeImpl::HasPinchZoomScrollbars() const {
   return pinch_zoom_scrollbar_horizontal_layer_id_ != Layer::INVALID_ID &&
          pinch_zoom_scrollbar_vertical_layer_id_ != Layer::INVALID_ID;
 }
 
 void LayerTreeImpl::UpdateRootScrollLayerSizeDelta() {
   LayerImpl* root_scroll = RootScrollLayer();
   LayerImpl* root_clip = RootClipLayer();
   DCHECK(root_scroll);
   DCHECK(root_clip);
   DCHECK(IsActiveTree());
 
   gfx::Vector2dF scrollable_viewport_size =
       gfx::RectF(ScrollableViewportSize()).bottom_right() - gfx::PointF();
 
   gfx::Vector2dF original_viewport_size =
       gfx::RectF(root_clip->bounds()).bottom_right() -
       gfx::PointF();
   original_viewport_size.Scale(1 / page_scale_factor());
 
   root_scroll->SetFixedContainerSizeDelta(
       scrollable_viewport_size - original_viewport_size);
 }
 
 }  // namespace cc