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

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index d42ec311f966c4dcbd32cfc7f166dc3f64ef90f8..03333a4ad88feb44a42f02b026ca94a45049d47c 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -42,6 +42,8 @@ LayerImpl::LayerImpl(LayerTreeImpl* tree_impl, int id)
       scrollable_(false),
       should_scroll_on_main_thread_(false),
       have_wheel_event_handlers_(false),
+      user_scrollable_horizontal_(true),
+      user_scrollable_vertical_(true),
       background_color_(0),
       stacking_order_changed_(false),
       double_sided_(true),
@@ -341,6 +343,15 @@ void LayerImpl::SetSentScrollDelta(gfx::Vector2d sent_scroll_delta) {
 
 gfx::Vector2dF LayerImpl::ScrollBy(gfx::Vector2dF scroll) {
   DCHECK(scrollable());
+  gfx::Vector2dF scroll_hidden;
+  if (!user_scrollable_horizontal_) {
+    scroll_hidden.set_x(scroll.x());
+    scroll.set_x(0.f);
+  }
+  if (!user_scrollable_vertical_) {
+    scroll_hidden.set_y(scroll.y());
+    scroll.set_y(0.f);
+  }
 
   gfx::Vector2dF min_delta = -scroll_offset_;
   gfx::Vector2dF max_delta = max_scroll_offset_ - scroll_offset_;
@@ -348,7 +359,8 @@ gfx::Vector2dF LayerImpl::ScrollBy(gfx::Vector2dF scroll) {
   gfx::Vector2dF new_delta = (ScrollDelta() + scroll);
   new_delta.SetToMax(min_delta);
   new_delta.SetToMin(max_delta);
-  gfx::Vector2dF unscrolled = ScrollDelta() + scroll - new_delta;
+  gfx::Vector2dF unscrolled =
+      ScrollDelta() + scroll + scroll_hidden - new_delta;
   SetScrollDelta(new_delta);
   return unscrolled;
 }
@@ -449,6 +461,9 @@ InputHandler::ScrollStatus LayerImpl::TryScroll(
     return InputHandler::ScrollIgnored;
   }
 
+  if (!user_scrollable_horizontal_ && !user_scrollable_vertical_)
+    return InputHandler::ScrollIgnored;

[jamesr, 2013/10/21 22:36:34]

nit: it'd be useful to TRACE_EVENT this bail-out like the other ones so it's
easier to diagnose failure-to-scroll issues

[sadrul, 2013/10/21 23:11:17]

Done.

+
   return InputHandler::ScrollStarted;
 }
 
@@ -514,6 +529,8 @@ void LayerImpl::PushPropertiesTo(LayerImpl* layer) {
   layer->SetTransform(transform_);
 
   layer->SetScrollable(scrollable_);
+  layer->SetUserScrollable(user_scrollable_horizontal_,
+                           user_scrollable_vertical_);
   layer->SetScrollOffsetAndDelta(
       scroll_offset_, layer->ScrollDelta() - layer->sent_scroll_delta());
   layer->SetSentScrollDelta(gfx::Vector2d());