Handle touchpad flings with passive event listeners on compositor thread.

content/renderer/input/input_event_filter.cc

Index: content/renderer/input/input_event_filter.cc
diff --git a/content/renderer/input/input_event_filter.cc b/content/renderer/input/input_event_filter.cc
index a82f2f76dc28bddaebd366a0da6a7f04da4ba96f..d4d918c73a24cc5ae0e5bb9fb642e275fbb733cb 100644
--- a/content/renderer/input/input_event_filter.cc
+++ b/content/renderer/input/input_event_filter.cc
@@ -108,6 +108,18 @@ void InputEventFilter::DidStopFlinging(int routing_id) {
   SendMessage(base::MakeUnique<InputHostMsg_DidStopFlinging>(routing_id));
 }
 
+void InputEventFilter::DispatchNonBlockingEventToMainThread(
+    int routing_id,
+    ui::ScopedWebInputEvent event) {
+  DCHECK(target_task_runner_->BelongsToCurrentThread());
+  RouteQueueMap::iterator iter = route_queues_.find(routing_id);
+  if (iter != route_queues_.end()) {
+    iter->second->HandleEvent(std::move(event), ui::LatencyInfo(),

[tdresser, 2016/09/14 18:58:07]

I'm worried we might accidentally use this on a non-synthetic event, and then
end up with bogus LatencyInfo.

Options:
1) Rename to make it clear this is synthetic.
2) Pass an empty LatencyInfo along from the callsite.
3) Hope this never happens.

I'm in favor of #2.

[dtapuska, 2016/09/15 20:43:04]

Approach #2 done.

+                              DISPATCH_TYPE_NON_BLOCKING,
+                              INPUT_EVENT_ACK_STATE_SET_NON_BLOCKING);
+  }
+}
+
 void InputEventFilter::NotifyInputEventHandled(int routing_id,
                                                blink::WebInputEvent::Type type,
                                                InputEventAckState ack_result) {