Scrollbars should get notifications from all scrollable layers up to container.

cc/layers/scrollbar_layer_impl_base.cc

 // Copyright 2013 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/layers/scrollbar_layer_impl_base.h"
 
 #include <algorithm>
 #include "cc/trees/layer_tree_impl.h"
 #include "ui/gfx/rect_conversions.h"
 
@@ skipping 29 matching lines @@
 void ScrollbarLayerImplBase::PushScrollClipPropertiesTo(LayerImpl* layer) {
   DCHECK(layer->ToScrollbarLayer());
   layer->ToScrollbarLayer()->SetScrollLayerById(ScrollLayerId());
   layer->ToScrollbarLayer()->SetClipLayerById(ClipLayerId());
 }
 
 ScrollbarLayerImplBase* ScrollbarLayerImplBase::ToScrollbarLayer() {
   return this;
 }
 
+namespace {
+
+typedef void (LayerImpl::*ScrollbarRegistrationOperation)(
+    ScrollbarLayerImplBase*);
+
+void RegisterScrollbarWithLayers(ScrollbarLayerImplBase* scrollbar,
+                                 LayerImpl* container_layer,
+                                 LayerImpl* scroll_layer,
+                                 ScrollbarRegistrationOperation operation) {
+  if (!container_layer || !scroll_layer)
+    return;
+
+  DCHECK(scrollbar);
+
+  // Scrollbars must be notifed of changes to their scroll and container layers
+  // and all scrollable layers in between.
+  for (LayerImpl* current_layer = scroll_layer;
+       current_layer && current_layer != container_layer->parent();
+       current_layer = current_layer->parent()) {
+    // TODO(wjmaclean) We shouldn't need to exempt the scroll_layer from the
+    // scrollable() test below. https://crbug.com/367858.
+    if (current_layer->scrollable() || current_layer == container_layer ||
+        current_layer == scroll_layer)
+      (current_layer->*operation)(scrollbar);
+  }
+}
+}  // namespace
+
 void ScrollbarLayerImplBase::SetScrollLayerById(int id) {
   LayerImpl* scroll_layer = layer_tree_impl()->LayerById(id);
   if (scroll_layer_ == scroll_layer)
     return;
 
-  if (scroll_layer_)
-    scroll_layer_->RemoveScrollbar(this);
+  RegisterScrollbarWithLayers(
+      this, clip_layer_, scroll_layer_, &LayerImpl::RemoveScrollbar);
   scroll_layer_ = scroll_layer;
-  if (scroll_layer_)
-    scroll_layer_->AddScrollbar(this);
+  RegisterScrollbarWithLayers(
+      this, clip_layer_, scroll_layer_, &LayerImpl::AddScrollbar);
 }
 
 void ScrollbarLayerImplBase::SetClipLayerById(int id) {
   LayerImpl* clip_layer = layer_tree_impl()->LayerById(id);
   if (clip_layer_ == clip_layer)
     return;
 
-  if (clip_layer_)
-    clip_layer_->RemoveScrollbar(this);
+  RegisterScrollbarWithLayers(
+      this, clip_layer_, scroll_layer_, &LayerImpl::RemoveScrollbar);
   clip_layer_ = clip_layer;
-  if (clip_layer_)
-    clip_layer_->AddScrollbar(this);
+  RegisterScrollbarWithLayers(
+      this, clip_layer_, scroll_layer_, &LayerImpl::AddScrollbar);
 }
 
 gfx::Rect ScrollbarLayerImplBase::ScrollbarLayerRectToContentRect(
     const gfx::RectF& layer_rect) const {
   // Don't intersect with the bounds as in LayerRectToContentRect() because
   // layer_rect here might be in coordinates of the containing layer.
   gfx::RectF content_rect = gfx::ScaleRect(layer_rect,
       contents_scale_x(),
       contents_scale_y());
   return gfx::ToEnclosingRect(content_rect);
@@ skipping 133 matching lines @@
 }
 
 void ScrollbarLayerImplBase::ScrollbarParametersDidChange() {
   if (!clip_layer_ || !scroll_layer_)
     return;
 
   scroll_layer_->SetScrollbarPosition(this, clip_layer_);
 }
 
 }  // namespace cc