Add initial CC support for scroll-blocks-on

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index 398ef81895ae08bc199b823c30c9bd27861a3c29..1a1046959e062e7fb368f9f803a85404789395e3 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -469,16 +469,39 @@ bool LayerTreeHostImpl::HaveWheelEventHandlersAt(
   return layer_impl != NULL;
 }
 
-bool LayerTreeHostImpl::HaveTouchEventHandlersAt(
-    const gfx::Point& viewport_point) {
+static LayerImpl* NextScrollLayer(LayerImpl* layer) {
+  if (LayerImpl* scroll_parent = layer->scroll_parent())
+    return scroll_parent;
+  return layer->parent();
+}
 
+static ScrollBlocksOn EffectiveScrollBlocksOn(LayerImpl* layer) {
+  ScrollBlocksOn blocks = ScrollBlocksOnNone;
+  for (; layer; layer = NextScrollLayer(layer)) {
+    blocks |= layer->scroll_blocks_on();
+  }
+  return blocks;
+}
+
+bool LayerTreeHostImpl::DoTouchEventsBlockScrollAt(
+    const gfx::Point& viewport_point) {
   gfx::PointF device_viewport_point =
       gfx::ScalePoint(viewport_point, device_scale_factor_);
 
+  // First check if scrolling at this point is required to block on any
+  // touch event handlers.  Note that we must start at the innermost layer
+  // (as opposed to only the layer found to contain a touch handler region
+  // below) to ensure all relevant scroll-blocks-on values are applied.
   LayerImpl* layer_impl =
-      active_tree_->FindLayerThatIsHitByPointInTouchHandlerRegion(
-          device_viewport_point);
+      active_tree_->FindLayerThatIsHitByPoint(device_viewport_point);
+  ScrollBlocksOn blocking = EffectiveScrollBlocksOn(layer_impl);
+  if (!(blocking & ScrollBlocksOnStartTouch))
+    return false;
 
+  // Now determine if there are actually any handlers at that point.
+  // TODO(rbyers): Consider also honoring touch-action (crbug.com/347272).
+  layer_impl = active_tree_->FindLayerThatIsHitByPointInTouchHandlerRegion(
+      device_viewport_point);
   return layer_impl != NULL;
 }
 
@@ -2255,12 +2278,6 @@ void LayerTreeHostImpl::BindToClient(InputHandlerClient* client) {
   input_handler_client_ = client;
 }
 
-static LayerImpl* NextScrollLayer(LayerImpl* layer) {
-  if (LayerImpl* scroll_parent = layer->scroll_parent())
-    return scroll_parent;
-  return layer->parent();
-}
-
 LayerImpl* LayerTreeHostImpl::FindScrollLayerForDeviceViewportPoint(
     const gfx::PointF& device_viewport_point,
     InputHandler::ScrollInputType type,
@@ -2269,12 +2286,15 @@ LayerImpl* LayerTreeHostImpl::FindScrollLayerForDeviceViewportPoint(
     bool* optional_has_ancestor_scroll_handler) const {
   DCHECK(scroll_on_main_thread);
 
+  ScrollBlocksOn block_mode = EffectiveScrollBlocksOn(layer_impl);
+
   // Walk up the hierarchy and look for a scrollable layer.
   LayerImpl* potentially_scrolling_layer_impl = NULL;
   for (; layer_impl; layer_impl = NextScrollLayer(layer_impl)) {
     // The content layer can also block attempts to scroll outside the main
     // thread.
-    ScrollStatus status = layer_impl->TryScroll(device_viewport_point, type);
+    ScrollStatus status =
+        layer_impl->TryScroll(device_viewport_point, type, block_mode);
     if (status == ScrollOnMainThread) {
       *scroll_on_main_thread = true;
       return NULL;
@@ -2284,7 +2304,8 @@ LayerImpl* LayerTreeHostImpl::FindScrollLayerForDeviceViewportPoint(
     if (!scroll_layer_impl)
       continue;
 
-    status = scroll_layer_impl->TryScroll(device_viewport_point, type);
+    status =
+        scroll_layer_impl->TryScroll(device_viewport_point, type, block_mode);
     // If any layer wants to divert the scroll event to the main thread, abort.
     if (status == ScrollOnMainThread) {
       *scroll_on_main_thread = true;