Add id properties to PointerEvent

We add id to PointerDetails which will be used as PointerEvent's pointerId, so we can use it
to keep the id from lower level events from each OS.

In this patch, we also remove touch_id from ui::TouchEvent and pointer_id from ui::PointerEvent,
which are redundant to this new id.

BUG=685817

Review-Url: https://codereview.chromium.org/2655303004
Cr-Commit-Position: refs/heads/master@{#450807}
diff --git a/ui/chromeos/touch_accessibility_enabler.cc b/ui/chromeos/touch_accessibility_enabler.cc
index 07d5c80..6e23f4bf 100644
--- a/ui/chromeos/touch_accessibility_enabler.cc
+++ b/ui/chromeos/touch_accessibility_enabler.cc
@@ -60,7 +60,7 @@
   DCHECK(!(event.flags() & ui::EF_TOUCH_ACCESSIBILITY));
   const ui::EventType type = event.type();
   const gfx::PointF& location = event.location_f();
-  const int touch_id = event.touch_id();
+  const int touch_id = event.pointer_details().id;
 
   if (type == ui::ET_TOUCH_PRESSED) {
     touch_locations_.insert(std::pair<int, gfx::PointF>(touch_id, location));