Make sure send one WebTouchEvent ack per ui::TouchEvent

content/browser/renderer_host/render_widget_host_view_aura.cc

Index: content/browser/renderer_host/render_widget_host_view_aura.cc
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.cc b/content/browser/renderer_host/render_widget_host_view_aura.cc
index fd85fcc8745cdf59c93e87322518bda129aff961..7eababfb57781f04050ffd1048ebc03639c2ba94 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.cc
+++ b/content/browser/renderer_host/render_widget_host_view_aura.cc
@@ -805,6 +805,18 @@ void RenderWidgetHostViewAura::ParentHierarchyChanged() {
   HandleParentBoundsChanged();
 }
 
+void RenderWidgetHostViewAura::MarkUnchangedTouchPointsAsStationary(
+    blink::WebTouchEvent* event,
+    int changed_touch_id) {
+  if (event->type == blink::WebInputEvent::TouchMove ||
+      event->type == blink::WebInputEvent::TouchCancel) {
+    for (size_t i = 0; i < event->touchesLength; ++i) {
+      if (event->touches[i].id != changed_touch_id)
+        event->touches[i].state = blink::WebTouchPoint::StateStationary;
+    }
+  }
+}
+
 void RenderWidgetHostViewAura::MovePluginWindows(
     const std::vector<WebPluginGeometry>& plugin_window_moves) {
 #if defined(OS_WIN)
@@ -1282,10 +1294,14 @@ void RenderWidgetHostViewAura::ProcessAckedTouchEvent(
       break;
   }
 
-  // Only send acks for changed touches.
+  // Only send acks for one changed touch point.
+  bool sent_ack = false;
   for (size_t i = 0; i < touch.event.touchesLength; ++i) {
-    if (touch.event.touches[i].state == required_state)
+    if (touch.event.touches[i].state == required_state) {
+      DCHECK(!sent_ack);
       host->dispatcher()->ProcessedTouchEvent(window_, result);
+      sent_ack = true;
+    }
   }
 }
 
@@ -2184,6 +2200,10 @@ void RenderWidgetHostViewAura::OnTouchEvent(ui::TouchEvent* event) {
   // processed by the gesture recognizer before events currently awaiting
   // dispatch in the touch queue.
   event->DisableSynchronousHandling();
+
+  // Set unchange touch point to StateStationary for touchmove and
+  // touchcancel to make sure only send one ack per WebTouchEvent.
+  MarkUnchangedTouchPointsAsStationary(&touch_event, event->touch_id());
   host_->ForwardTouchEventWithLatencyInfo(touch_event, *event->latency());
 }