Don't send touchcancel on touch scroll start

content/browser/renderer_host/input/touch_event_queue.h

 // 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_
 
 #include <deque>
 #include <map>
 
@@ skipping 20 matching lines @@
 
   virtual void OnTouchEventAck(
       const TouchEventWithLatencyInfo& event,
       InputEventAckState ack_result) = 0;
 };
 
 // A queue for throttling and coalescing touch-events.
 class CONTENT_EXPORT TouchEventQueue {
  public:
   // Different ways of dealing with touch events during scrolling.
-  // TODO(rbyers): Remove (or otherwise update) this once results of
-  // experiments are complete.  http://crbug.com/328503
+  // TODO(rbyers): Remove this once we're confident that touch move absorption
+  // is OK. http://crbug.com/350430
   enum TouchScrollingMode {
     // Send a touchcancel on scroll start and no further touch events for the
     // duration of the scroll.  Chrome Android's traditional behavior.
     TOUCH_SCROLLING_MODE_TOUCHCANCEL,
     // Send touchmove events throughout a scroll, blocking on each ACK and
     // using the disposition to determine whether a scroll update should be
     // sent.  Mobile Safari's default overflow scroll behavior.
     TOUCH_SCROLLING_MODE_SYNC_TOUCHMOVE,
     // Like sync, except that consumed scroll events cause subsequent touchmove
     // events to be suppressed.  Unconsumed scroll events return touchmove
     // events to being dispatched synchronously (so scrolling may be hijacked
-    // when a scroll limit is reached, and later resumed).
+    // when a scroll limit is reached, and later resumed). http://goo.gl/RShsdN
     TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE,
-    TOUCH_SCROLLING_MODE_DEFAULT = TOUCH_SCROLLING_MODE_TOUCHCANCEL
+    TOUCH_SCROLLING_MODE_DEFAULT = TOUCH_SCROLLING_MODE_ABSORB_TOUCHMOVE
   };
 
   // The |client| must outlive the TouchEventQueue. If
   // |touchmove_suppression_length_dips| <= 0, touch move suppression is
   // disabled.
   TouchEventQueue(TouchEventQueueClient* client,
                   TouchScrollingMode mode,
                   double touchmove_suppression_length_dips);
   ~TouchEventQueue();
 
@@ skipping 132 matching lines @@
   // setting for experimentation, but we may evolve it into an app-controlled
   // mode.
   const TouchScrollingMode touch_scrolling_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchEventQueue);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_INPUT_TOUCH_EVENT_QUEUE_H_