Add id properties to PointerEvent

ui/events/blink/web_input_event_builders_win.cc

Index: ui/events/blink/web_input_event_builders_win.cc
diff --git a/ui/events/blink/web_input_event_builders_win.cc b/ui/events/blink/web_input_event_builders_win.cc
index fbeb14cf3c15670455019c6da0dd8984af0da891..d3a2651fe9a7fcbcc5e4d541a4b32a3883a03679 100644
--- a/ui/events/blink/web_input_event_builders_win.cc
+++ b/ui/events/blink/web_input_event_builders_win.cc
@@ -167,9 +167,9 @@ WebMouseEvent WebMouseEventBuilder::Build(
   WebMouseEvent result(type, modifiers, time_stamp);
   result.pointerType = pointer_type;
   result.button = button;
+  result.id = ui::PointerEvent::kMousePointerId;

[mustaq, 2017/02/27 16:02:26]

Are we sure that stylus events are not going through this? Hardcoded ids could
cause problems with stylus ids, even after we migrate to WM_POINTER events
because legacy systems could still pass stylus events as WM_MOUSE events.

 
   // set position fields:
-
   result.x = static_cast<short>(LOWORD(lparam));
   result.y = static_cast<short>(HIWORD(lparam));
   result.windowX = result.x;