cc: Do not allow gesture-scrolling 'overflow[-{x|y}]:hidden' layers.

cc/layers/layer_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/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/strings/stringprintf.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/scrollbar_animation_controller.h"
@@ skipping 323 matching lines @@
   DCHECK(layer_tree_impl()->IsActiveTree());
 
   if (sent_scroll_delta_ == sent_scroll_delta)
     return;
 
   sent_scroll_delta_ = sent_scroll_delta;
 }
 
 gfx::Vector2dF LayerImpl::ScrollBy(gfx::Vector2dF scroll) {
   DCHECK(scrollable());
+  if (!horizontal_scrollbar_layer_)
+    scroll.set_x(0.f);

[danakj, 2013/10/21 15:14:42]

This would eat the whole scroll but not perform it, ie return unscrolled would
return 0 along this axis. Is that the intent here?

[sadrul, 2013/10/21 16:19:14]

That wasn't intentional. Fixed. Thanks!

+  if (!vertical_scrollbar_layer_)
+    scroll.set_y(0.f);
 
   gfx::Vector2dF min_delta = -scroll_offset_;
   gfx::Vector2dF max_delta = max_scroll_offset_ - scroll_offset_;
   // Clamp new_delta so that position + delta stays within scroll bounds.
   gfx::Vector2dF new_delta = (ScrollDelta() + scroll);
   new_delta.SetToMax(min_delta);
   new_delta.SetToMin(max_delta);
   gfx::Vector2dF unscrolled = ScrollDelta() + scroll - new_delta;
   SetScrollDelta(new_delta);
   return unscrolled;
@@ skipping 88 matching lines @@
     return InputHandler::ScrollIgnored;
   }
 
   if (max_scroll_offset_.x() <= 0 && max_scroll_offset_.y() <= 0) {
     TRACE_EVENT0("cc",
                  "LayerImpl::tryScroll: Ignored. Technically scrollable,"
                  " but has no affordance in either direction.");
     return InputHandler::ScrollIgnored;
   }
 
+  if (!horizontal_scrollbar_layer_ && !vertical_scrollbar_layer_)
+    return InputHandler::ScrollIgnored;
+
   return InputHandler::ScrollStarted;
 }
 
 bool LayerImpl::DrawCheckerboardForMissingTiles() const {
   return draw_checkerboard_for_missing_tiles_ &&
       !layer_tree_impl()->settings().background_color_instead_of_checkerboard;
 }
 
 gfx::Rect LayerImpl::LayerRectToContentRect(
     const gfx::RectF& layer_rect) const {
@@ skipping 843 matching lines @@
 
 size_t LayerImpl::GPUMemoryUsageInBytes() const { return 0; }
 
 scoped_ptr<base::Value> LayerImpl::AsValue() const {
   scoped_ptr<base::DictionaryValue> state(new base::DictionaryValue());
   AsValueInto(state.get());
   return state.PassAs<base::Value>();
 }
 
 }  // namespace cc