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..cd391cc075c29ac5aabaa9e028f97d49bb4b4a4f 100644
--- a/content/renderer/input/input_handler_manager.cc
+++ b/content/renderer/input/input_handler_manager.cc
@@ -134,6 +134,7 @@ void InputHandlerManager::ObserveWheelEventAndResultOnCompositorThread(
     int routing_id,
     const blink::WebMouseWheelEvent& wheel_event,
     const cc::InputHandlerScrollResult& scroll_result) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
   auto it = input_handlers_.find(routing_id);
   if (it == input_handlers_.end())
     return;
@@ -144,6 +145,32 @@ void InputHandlerManager::ObserveWheelEventAndResultOnCompositorThread(
       wheel_event, scroll_result);
 }
 
+void InputHandlerManager::ObserveGestureEventAndResultOnMainThread(
+    int routing_id,
+    const blink::WebGestureEvent& gesture_event,
+    const cc::InputHandlerScrollResult& scroll_result) {
+  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) {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  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) {