Addressing sadruls comments from the previous CL https://codereview.chromium.org/22865036/ which was

ui/aura/root_window.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/aura/root_window.h"
 
 #include <vector>
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ skipping 209 matching lines @@
          event.type() == ui::ET_GESTURE_TAP_DOWN);
   // We allow for only one outstanding repostable event. This is used
   // in exiting context menus.  A dropped repost request is allowed.
   if (event.type() == ui::ET_MOUSE_PRESSED) {
     held_repostable_event_.reset(
         new ui::MouseEvent(
             static_cast<const ui::MouseEvent&>(event),
             static_cast<aura::Window*>(event.target()),
             static_cast<aura::Window*>(this)));
   } else {
-    const ui::GestureEvent* gesture_event =
-        static_cast<const ui::GestureEvent*>(&event);
-    held_repostable_event_.reset(new ui::GestureEvent(
-        gesture_event->type(),
-        gesture_event->root_location().x(),
-        gesture_event->root_location().y(),
-        gesture_event->flags(),
-        gesture_event->time_stamp(),
-        gesture_event->details(),
-        gesture_event->touch_ids_bitfield()));
+    held_repostable_event_.reset(
+        new ui::GestureEvent(
+            static_cast<const ui::GestureEvent&>(event),
+            static_cast<aura::Window*>(event.target()),
+            static_cast<aura::Window*>(this)));
   }
   base::MessageLoop::current()->PostTask(
       FROM_HERE,
       base::Bind(&RootWindow::DispatchHeldEvents,
                   repostable_event_factory_.GetWeakPtr()));
 }
 
 RootWindowHostDelegate* RootWindow::AsRootWindowHostDelegate() {
   return this;
 }
@@ skipping 776 matching lines @@
   if (event->type() != ui::ET_GESTURE_TAP_DOWN)
     return false;
 
   // Cleanup stale gesture events for the old gesture target.
   GestureConsumer* old_consumer = GetGestureTarget(event);
   if (old_consumer)
     CleanupGestureRecognizerState(static_cast<aura::Window*>(old_consumer));
 
   Window* new_consumer = GetEventHandlerForPoint(event->root_location());
   if (new_consumer) {
+    ui::GestureEvent begin_gesture(
+        ui::ET_GESTURE_BEGIN,
+        event->x(),
+        event->y(),
+        event->flags(),
+        event->time_stamp(),
+        ui::GestureEventDetails(ui::ET_GESTURE_BEGIN, 0, 0),
+        event->touch_ids_bitfield());
+    ProcessEvent(new_consumer, &begin_gesture);
     ProcessEvent(new_consumer, event);
     return event->handled();
   }
   return false;
 }
 
 bool RootWindow::DispatchMouseEventToTarget(ui::MouseEvent* event,
                                             Window* target) {
   client::CursorClient* cursor_client = client::GetCursorClient(this);
   if (cursor_client &&
@@ skipping 173 matching lines @@
 }
 
 gfx::Transform RootWindow::GetInverseRootTransform() const {
   float scale = ui::GetDeviceScaleFactor(layer());
   gfx::Transform transform;
   transform.Scale(1.0f / scale, 1.0f / scale);
   return transformer_->GetInverseTransform() * transform;
 }
 
 }  // namespace aura