Support vsync-aligned wheel event dispatch

content/browser/renderer_host/input/input_router_impl.cc

Index: content/browser/renderer_host/input/input_router_impl.cc
diff --git a/content/browser/renderer_host/input/input_router_impl.cc b/content/browser/renderer_host/input/input_router_impl.cc
index 8ecb37b4567999373caaed93e7c86cf445a09a7e..32297fcf5866e18d76d1a4373c9b4b4b4b41ca5a 100644
--- a/content/browser/renderer_host/input/input_router_impl.cc
+++ b/content/browser/renderer_host/input/input_router_impl.cc
@@ -10,10 +10,8 @@
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
-#include "content/browser/renderer_host/input/gesture_event_queue.h"
 #include "content/browser/renderer_host/input/input_ack_handler.h"
 #include "content/browser/renderer_host/input/input_router_client.h"
-#include "content/browser/renderer_host/input/touch_event_queue.h"
 #include "content/browser/renderer_host/input/touchpad_tap_suppression_controller.h"
 #include "content/common/content_constants_internal.h"
 #include "content/common/edit_command.h"
@@ -57,7 +55,7 @@ const char* GetEventAckName(InputEventAckState ack_result) {
 
 } // namespace
 
-InputRouterImpl::Config::Config() {}
+InputRouterImpl::Config::Config() : buffer_wheel_events_until_flush(false) {}
 
 InputRouterImpl::InputRouterImpl(IPC::Sender* sender,
                                  InputRouterClient* client,
@@ -71,12 +69,12 @@ InputRouterImpl::InputRouterImpl(IPC::Sender* sender,
       select_message_pending_(false),
       move_caret_pending_(false),
       mouse_move_pending_(false),
-      mouse_wheel_pending_(false),
       current_ack_source_(ACK_SOURCE_NONE),
       flush_requested_(false),
       active_renderer_fling_count_(0),
       touch_event_queue_(this, config.touch_config),
-      gesture_event_queue_(this, this, config.gesture_config) {
+      gesture_event_queue_(this, this, config.gesture_config),
+      wheel_event_queue_(this, config.buffer_wheel_events_until_flush) {
   DCHECK(sender);
   DCHECK(client);
   DCHECK(ack_handler);
@@ -106,6 +104,9 @@ bool InputRouterImpl::SendInput(scoped_ptr<IPC::Message> message) {
 
 void InputRouterImpl::FlushInput(base::TimeTicks flush_time) {
   flush_requested_ = true;
+
+  wheel_event_queue_.Flush();
+
   SignalFlushedIfNecessary();
 }
 
@@ -125,38 +126,7 @@ void InputRouterImpl::SendMouseEvent(
 
 void InputRouterImpl::SendWheelEvent(
     const MouseWheelEventWithLatencyInfo& wheel_event) {
-  if (mouse_wheel_pending_) {
-    // If there's already a mouse wheel event waiting to be sent to the
-    // renderer, add the new deltas to that event. Not doing so (e.g., by
-    // dropping the old event, as for mouse moves) results in very slow
-    // scrolling on the Mac.
-    if (wheel_event.event.hasPreciseScrollingDeltas)
-      DCHECK(wheel_event.event.canScroll);
-    DCHECK(!(wheel_event.event.hasPreciseScrollingDeltas &&
-             !wheel_event.event.canScroll));
-    if (coalesced_mouse_wheel_events_.empty() ||
-        (!coalesced_mouse_wheel_events_.empty() &&
-         !coalesced_mouse_wheel_events_.back().CanCoalesceWith(wheel_event))) {
-      coalesced_mouse_wheel_events_.push_back(wheel_event);
-    } else {
-      coalesced_mouse_wheel_events_.back().CoalesceWith(wheel_event);
-      TRACE_EVENT_INSTANT2("input", "InputRouterImpl::CoalescedWheelEvent",
-                           TRACE_EVENT_SCOPE_THREAD,
-                           "total_dx",
-                           coalesced_mouse_wheel_events_.back().event.deltaX,
-                           "total_dy",
-                           coalesced_mouse_wheel_events_.back().event.deltaY);
-    }
-    return;
-  }
-
-  mouse_wheel_pending_ = true;
-  current_wheel_event_ = wheel_event;
-
-  LOCAL_HISTOGRAM_COUNTS_100("Renderer.WheelQueueSize",
-                             coalesced_mouse_wheel_events_.size());
-
-  FilterAndSendWebInputEvent(wheel_event.event, wheel_event.latency);
+  wheel_event_queue_.QueueEvent(wheel_event);
 }
 
 void InputRouterImpl::SendKeyboardEvent(
@@ -250,8 +220,8 @@ bool InputRouterImpl::HasPendingEvents() const {
   return !touch_event_queue_.empty() ||
          !gesture_event_queue_.empty() ||
          !key_queue_.empty() ||
+         !wheel_event_queue_.empty() ||
          mouse_move_pending_ ||
-         mouse_wheel_pending_ ||
          select_message_pending_ ||
          move_caret_pending_ ||
          active_renderer_fling_count_ > 0;
@@ -296,6 +266,21 @@ void InputRouterImpl::OnGestureEventAck(
   ack_handler_->OnGestureEventAck(event, ack_result);
 }
 
+void InputRouterImpl::SendWheelEventImmediately(
+    const MouseWheelEventWithLatencyInfo& wheel_event) {
+  FilterAndSendWebInputEvent(wheel_event.event, wheel_event.latency);
+}
+
+void InputRouterImpl::OnWheelEventAck(
+    const MouseWheelEventWithLatencyInfo& event,
+    InputEventAckState ack_result) {
+  ack_handler_->OnWheelEventAck(event, ack_result);
+}
+
+void InputRouterImpl::SetNeedsFlush() {
+  client_->SetNeedsFlushInput();
+}
+
 bool InputRouterImpl::SendSelectMessage(
     scoped_ptr<IPC::Message> message) {
   DCHECK(message->type() == InputMsg_SelectRange::ID ||
@@ -581,27 +566,7 @@ void InputRouterImpl::ProcessMouseAck(blink::WebInputEvent::Type type,
 
 void InputRouterImpl::ProcessWheelAck(InputEventAckState ack_result,
                                       const ui::LatencyInfo& latency) {
-  // TODO(miletus): Add renderer side latency to each uncoalesced mouse
-  // wheel event and add terminal component to each of them.
-  current_wheel_event_.latency.AddNewLatencyFrom(latency);
-
-  // Process the unhandled wheel event here before calling SendWheelEvent()
-  // since it will mutate current_wheel_event_.
-  ack_handler_->OnWheelEventAck(current_wheel_event_, ack_result);
-
-  // Mark the wheel event complete only after the ACKs have been handled above.
-  // For example, ACKing the GesturePinchUpdate could cause another
-  // GesturePinchUpdate to be sent, which should queue a wheel event rather than
-  // send it immediately.
-  mouse_wheel_pending_ = false;
-
-  // Send the next (coalesced or synthetic) mouse wheel event.
-  if (!coalesced_mouse_wheel_events_.empty()) {
-    MouseWheelEventWithLatencyInfo next_wheel_event =
-        coalesced_mouse_wheel_events_.front();
-    coalesced_mouse_wheel_events_.pop_front();
-    SendWheelEvent(next_wheel_event);
-  }
+  wheel_event_queue_.ProcessWheelAck(ack_result, latency);
 }
 
 void InputRouterImpl::ProcessGestureAck(WebInputEvent::Type type,