Implement Wheel Gesture Scrolling on OSX.

content/renderer/input/input_handler_manager.cc

Index: content/renderer/input/input_handler_manager.cc
diff --git a/content/renderer/input/input_handler_manager.cc b/content/renderer/input/input_handler_manager.cc
index 58fd95f04f8b56f9287b1c9d50432436e84e12e0..ca2ee6fe7ac7fbca6ffc49946cb8df23a45e288e 100644
--- a/content/renderer/input/input_handler_manager.cc
+++ b/content/renderer/input/input_handler_manager.cc
@@ -144,6 +144,31 @@ void InputHandlerManager::ObserveWheelEventAndResultOnCompositorThread(
       wheel_event, scroll_result);
 }
 
+void InputHandlerManager::ObserveGestureEventAndResultOnMainThread(
+    int routing_id,
+    const blink::WebGestureEvent& gesture_event,
+    const cc::InputHandlerScrollResult& scroll_result) {

[tdresser, 2016/03/02 18:26:53]

Should we check that we're on the correct thread here?

[dtapuska, 2016/03/07 18:03:59]

I've added a check in the OnCompositorThread since that is an affirmative check;
adding it here OnMainThread might not be wise since task_runner_ could in-fact
be the same thread as the main thread.

+  task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(
+          &InputHandlerManager::ObserveGestureEventAndResultOnCompositorThread,
+          base::Unretained(this), routing_id, gesture_event, scroll_result));
+}
+
+void InputHandlerManager::ObserveGestureEventAndResultOnCompositorThread(
+    int routing_id,
+    const blink::WebGestureEvent& gesture_event,
+    const cc::InputHandlerScrollResult& scroll_result) {
+  auto it = input_handlers_.find(routing_id);
+  if (it == input_handlers_.end())
+    return;
+
+  InputHandlerProxy* proxy = it->second->input_handler_proxy();
+  DCHECK(proxy->scroll_elasticity_controller());
+  proxy->scroll_elasticity_controller()->ObserveGestureEventAndResult(
+      gesture_event, scroll_result);
+}
+
 void InputHandlerManager::NonBlockingInputEventHandledOnMainThread(
     int routing_id,
     blink::WebInputEvent::Type type) {