Prevent partial touch sequences from reaching the renderer

content/browser/renderer_host/input/touch_event_queue.h

Index: content/browser/renderer_host/input/touch_event_queue.h
diff --git a/content/browser/renderer_host/input/touch_event_queue.h b/content/browser/renderer_host/input/touch_event_queue.h
index aa211af8a649e6dfd5f233b55d17e203c99618d4..a79a33a56108866b9d82a9763cc56c2e0faeb634 100644
--- a/content/browser/renderer_host/input/touch_event_queue.h
+++ b/content/browser/renderer_host/input/touch_event_queue.h
@@ -82,7 +82,7 @@ class CONTENT_EXPORT TouchEventQueue {
   }
 
   bool has_handlers() const {
-    return has_handlers_;
+    return touch_handling_state_ != NO_TOUCH_HANDLER;
   }
 
  private:
@@ -133,15 +133,15 @@ class CONTENT_EXPORT TouchEventQueue {
   // ack after forwarding a touch event to the client.
   bool dispatching_touch_;
 
-  // Whether there are any registered touch handlers. Defaults to false.
-  bool has_handlers_;
-
-  // Don't send touch events to the renderer while scrolling.
-  bool scroll_in_progress_;
-
-  // Whether an event in the current (multi)touch sequence was consumed by the
-  // renderer.  The touch timeout will never be activated when this is true.
-  bool renderer_is_consuming_touch_gesture_;
+  // Determines touch event forwarding decisions.

[Rick Byers, 2014/01/21 22:00:25]

I like collapsing the bits into a single enum!  I think we should try to be
clear on TEQ's role here though.  In particular, I think of it as part of the
low-level of the platform, below gestures which are at a higher conceptual
level.  So I don't think we should be even mentioning "gesture" here.

Can we think of this more as a touch event filter optimization?  Eg. something
like (and this is probably mostly naming changes rather than semantic changes):

// Determines which touch events we can safely avoid sending
// to the renderer as a performance optimization.
enum TouchFilteringState {
  FORWARD_ALL_TOUCHES,    // Don't filter at all - the default
  FORWARD_TOUCHES_UNTIL_TIMEOUT,  // Don't filter unless we get an ACK timeout
  DROP_TOUCHES_IN_SEQUENCE,  // Filter all events until all active touch points
are released, then revert to sending everything.
  DROP_ALL_TOUCHES,     // Filter everything - eg. no touch handlers
}

In particular, this feels less coupled to the idea that a gesture is either
consumed or not (just thinking of how I'd change this for my experimental touch
scroll modes - https://codereview.chromium.org/140253005/, one of which we'll
probably land eventually).

[jdduke (slow), 2014/01/22 02:47:00]

That sounds just fine :) And I agree, using the term gesture here just leads to
confusion.  Too much borrowing of terms from ContentViewGestureHandler... 

+  enum TouchHandlingState {
+    HAS_TOUCH_HANDLER,             // All events forwarded.
+    NO_TOUCH_HANDLER,              // No events forwarded.
+    NO_TOUCH_HANDLER_FOR_GESTURE,  // No more events in the sequence forwarded.
+    RENDERER_CONSUMING_GESTURE,    // All events in the sequence forwarded.
+    TOUCH_HANDLING_STATE_DEFAULT = NO_TOUCH_HANDLER,
+  };
+  TouchHandlingState touch_handling_state_;
 
   // Optional handler for timed-out touch event acks, disabled by default.
   bool ack_timeout_enabled_;