Implement Wheel Gesture Scrolling on OSX.

ui/events/blink/input_handler_proxy.cc

Index: ui/events/blink/input_handler_proxy.cc
diff --git a/ui/events/blink/input_handler_proxy.cc b/ui/events/blink/input_handler_proxy.cc
index 187c9ac85a13cb26f002f2224f96bb42a7fcd13d..0af2a0f76de61aa24fe886455cac05778c85fe09 100644
--- a/ui/events/blink/input_handler_proxy.cc
+++ b/ui/events/blink/input_handler_proxy.cc
@@ -620,20 +620,40 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureScrollBegin(
   RecordMainThreadScrollingReasons(gesture_event.type,
                                    scroll_status.main_thread_scrolling_reasons);
 
+  InputHandlerProxy::EventDisposition result = DID_NOT_HANDLE;
   switch (scroll_status.thread) {
     case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
       TRACE_EVENT_INSTANT0("input",
                            "InputHandlerProxy::handle_input gesture scroll",
                            TRACE_EVENT_SCOPE_THREAD);
       gesture_scroll_on_impl_thread_ = true;
-      return DID_HANDLE;
+      result = DID_HANDLE;
+      break;
     case cc::InputHandler::SCROLL_UNKNOWN:
     case cc::InputHandler::SCROLL_ON_MAIN_THREAD:
-      return DID_NOT_HANDLE;
+      result = DID_NOT_HANDLE;
+      break;
     case cc::InputHandler::SCROLL_IGNORED:
-      return DROP_EVENT;
+      result = DROP_EVENT;
+      break;
   }
-  return DID_NOT_HANDLE;
+  // Send the event and its disposition to the elasticity controller to update
+  // the over-scroll animation. If the event is to be handled on the main
+  // thread, the event and its disposition will be sent to the elasticity
+  // controller after being handled on the main thread.
+  if (scroll_elasticity_controller_ && result != DID_NOT_HANDLE) {
+    // Note that the call to the elasticity controller is made asynchronously,
+    // to minimize divergence between main thread and impl thread event
+    // handling paths.
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(
+            &InputScrollElasticityController::ObserveGestureEventAndResult,
+            scroll_elasticity_controller_->GetWeakPtr(), gesture_event,
+            cc::InputHandlerScrollResult()));
+  }
+
+  return result;
 }
 
 InputHandlerProxy::EventDisposition
@@ -665,6 +685,21 @@ InputHandlerProxy::HandleGestureScrollUpdate(
   cc::InputHandlerScrollResult scroll_result =
       input_handler_->ScrollBy(&scroll_state);
   HandleOverscroll(scroll_point, scroll_result);
+
+  // Send the event and its disposition to the elasticity controller to update
+  // the over-scroll animation.
+  if (scroll_elasticity_controller_) {
+    // Note that the call to the elasticity controller is made asynchronously,
+    // to minimize divergence between main thread and impl thread event
+    // handling paths.
+    base::ThreadTaskRunnerHandle::Get()->PostTask(

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

Can we share this logic with HandleGestureScrollBegin/End?

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

Done.

+        FROM_HERE,
+        base::Bind(
+            &InputScrollElasticityController::ObserveGestureEventAndResult,
+            scroll_elasticity_controller_->GetWeakPtr(), gesture_event,
+            scroll_result));
+  }
+
   return scroll_result.did_scroll ? DID_HANDLE : DROP_EVENT;
 }
 
@@ -678,6 +713,23 @@ InputHandlerProxy::EventDisposition InputHandlerProxy::HandleGestureScrollEnd(
   input_handler_->ScrollEnd(&scroll_state);
   if (!gesture_scroll_on_impl_thread_)
     return DID_NOT_HANDLE;
+
+  // Send the event and its disposition to the elasticity controller to update
+  // the over-scroll animation. If the event is to be handled on the main
+  // thread, the event and its disposition will be sent to the elasticity
+  // controller after being handled on the main thread.
+  if (scroll_elasticity_controller_) {
+    // Note that the call to the elasticity controller is made asynchronously,
+    // to minimize divergence between main thread and impl thread event
+    // handling paths.
+    base::ThreadTaskRunnerHandle::Get()->PostTask(
+        FROM_HERE,
+        base::Bind(
+            &InputScrollElasticityController::ObserveGestureEventAndResult,
+            scroll_elasticity_controller_->GetWeakPtr(), gesture_event,
+            cc::InputHandlerScrollResult()));
+  }
+
   gesture_scroll_on_impl_thread_ = false;
   return DID_HANDLE;
 }