Don't send touchcancel on touch scroll start

cc/trees/layer_tree_host_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_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 2199 matching lines @@
 bool LayerTreeHostImpl::ScrollBy(const gfx::Point& viewport_point,
                                  const gfx::Vector2dF& scroll_delta) {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBy");
   if (!CurrentlyScrollingLayer())
     return false;
 
   gfx::Vector2dF pending_delta = scroll_delta;
   gfx::Vector2dF unused_root_delta;
   bool did_scroll_x = false;
   bool did_scroll_y = false;
+  bool did_scroll_top_controls = false;
   // TODO(wjmaclean) Should we guard against CurrentlyScrollingLayer() == 0
   // here?
   bool consume_by_top_controls =
       top_controls_manager_ &&
       (((CurrentlyScrollingLayer() == InnerViewportScrollLayer() ||
          CurrentlyScrollingLayer() == OuterViewportScrollLayer()) &&
         InnerViewportScrollLayer()->MaxScrollOffset().y() > 0) ||
        scroll_delta.y() < 0);
 
   for (LayerImpl* layer_impl = CurrentlyScrollingLayer();
        layer_impl;
        layer_impl = layer_impl->parent()) {
     if (!layer_impl->scrollable())
       continue;
 
     if (layer_impl == InnerViewportScrollLayer()) {
       // Only allow bubble scrolling when the scroll is in the direction to make
       // the top controls visible.
       gfx::Vector2dF applied_delta;
       gfx::Vector2dF excess_delta;
       if (consume_by_top_controls) {
         excess_delta = top_controls_manager_->ScrollBy(pending_delta);
         applied_delta = pending_delta - excess_delta;
         pending_delta = excess_delta;
         // Force updating of vertical adjust values if needed.
-        if (applied_delta.y() != 0)
+        if (applied_delta.y() != 0) {
+          did_scroll_top_controls = true;
           layer_impl->ScrollbarParametersDidChange();
+        }
       }
       // Track root layer deltas for reporting overscroll.
       unused_root_delta = pending_delta;
     }
 
     gfx::Vector2dF applied_delta;
     // Gesture events need to be transformed from viewport coordinates to local
     // layer coordinates so that the scrolling contents exactly follow the
     // user's finger. In contrast, wheel events represent a fixed amount of
     // scrolling so we can just apply them directly.
@@ skipping 43 matching lines @@
 
     // Allow further movement only on an axis perpendicular to the direction in
     // which the layer moved.
     gfx::Vector2dF perpendicular_axis(-applied_delta.y(), applied_delta.x());
     pending_delta = MathUtil::ProjectVector(pending_delta, perpendicular_axis);
 
     if (gfx::ToRoundedVector2d(pending_delta).IsZero())
       break;
   }
 
-  bool did_scroll = did_scroll_x || did_scroll_y;
-  if (did_scroll) {
+  bool did_scroll_content = did_scroll_x || did_scroll_y;
+  if (did_scroll_content) {
     client_->SetNeedsCommitOnImplThread();
     SetNeedsRedraw();
     client_->RenewTreePriority();
   }
 
   // Scrolling along an axis resets accumulated root overscroll for that axis.
   if (did_scroll_x)
     accumulated_root_overscroll_.set_x(0);
   if (did_scroll_y)
     accumulated_root_overscroll_.set_y(0);
 
   accumulated_root_overscroll_ += unused_root_delta;
   bool did_overscroll = !gfx::ToRoundedVector2d(unused_root_delta).IsZero();
   if (did_overscroll && input_handler_client_) {
     DidOverscrollParams params;
     params.accumulated_overscroll = accumulated_root_overscroll_;
     params.latest_overscroll_delta = unused_root_delta;
     params.current_fling_velocity = current_fling_velocity_;
     input_handler_client_->DidOverscroll(params);
   }
 
-  return did_scroll;
+  return did_scroll_content || did_scroll_top_controls;
 }
 
 // This implements scrolling by page as described here:
 // http://msdn.microsoft.com/en-us/library/windows/desktop/ms645601(v=vs.85).aspx#_win32_The_Mouse_Wheel
 // for events with WHEEL_PAGESCROLL set.
 bool LayerTreeHostImpl::ScrollVerticallyByPage(const gfx::Point& viewport_point,
                                                ScrollDirection direction) {
   DCHECK(wheel_scrolling_);
 
   for (LayerImpl* layer_impl = CurrentlyScrollingLayer();
@@ skipping 689 matching lines @@
   swap_promise_monitor_.erase(monitor);
 }
 
 void LayerTreeHostImpl::NotifySwapPromiseMonitorsOfSetNeedsRedraw() {
   std::set<SwapPromiseMonitor*>::iterator it = swap_promise_monitor_.begin();
   for (; it != swap_promise_monitor_.end(); it++)
     (*it)->OnSetNeedsRedrawOnImpl();
 }
 
 }  // namespace cc