Add pointer id to the WebMouseEvent's constructors

ui/events/event.h

 // 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.
 
 #ifndef UI_EVENTS_EVENT_H_
 #define UI_EVENTS_EVENT_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 463 matching lines @@
   int id = 0;
 
   // Only used by mouse wheel events. The amount to scroll. This is in multiples
   // of kWheelDelta.
   // Note: offset_.x() > 0/offset_.y() > 0 means scroll left/up.
   gfx::Vector2d offset;
 };
 
 class EVENTS_EXPORT MouseEvent : public LocatedEvent {
  public:
-  static const int32_t kMousePointerId;
+  static const int kMousePointerId;

[sky, 2017/05/05 22:51:46]

This value is serialized in mojom as an int32. It would be safer to convert
PointerDetails to use int32_t rather than changing this. See
https://chromium.googlesource.com/chromium/src/+/master/ui/events/mojo/event....

 
   explicit MouseEvent(const base::NativeEvent& native_event);
 
   // |pointer_event.IsMousePointerEvent()| must be true.
   // Note: If |pointer_event| is a mouse wheel pointer event, use the
   // MouseWheelEvent version of this function to convert to a MouseWheelEvent
   // instead.
   explicit MouseEvent(const PointerEvent& pointer_event);
 
   // Create a new MouseEvent based on the provided model.
@@ skipping 558 matching lines @@
   // dispatched. This field gets a non-zero value only for gestures that are
   // released through TouchDispositionGestureFilter::SendGesture. The gesture
   // events that aren't fired directly in response to processing a touch-event
   // (e.g. timer fired ones), this id is zero. See crbug.com/618738.
   uint32_t unique_touch_event_id_;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_H_