Add id properties to PointerEvent

ui/events/event.h

Index: ui/events/event.h
diff --git a/ui/events/event.h b/ui/events/event.h
index d07fc639222a4b78e672b850b5bf38d452603308..8671b643abc77ff9e40fee01c4cb0723ff7ed44f 100644
--- a/ui/events/event.h
+++ b/ui/events/event.h
@@ -408,10 +408,8 @@ class EVENTS_EXPORT LocatedEvent : public Event {
 // PointerEvents API.
 struct EVENTS_EXPORT PointerDetails {
  public:
-  PointerDetails() {}
-  explicit PointerDetails(EventPointerType pointer_type)
-      : pointer_type(pointer_type),
-        force(std::numeric_limits<float>::quiet_NaN()) {}
+  PointerDetails();
+  explicit PointerDetails(EventPointerType pointer_type);
   PointerDetails(EventPointerType pointer_type,
                  float radius_x,
                  float radius_y,
@@ -419,21 +417,10 @@ struct EVENTS_EXPORT PointerDetails {
                  float tilt_x,
                  float tilt_y,
                  float tangential_pressure = 0.0f,
-                 int twist = 0)
-      : pointer_type(pointer_type),
-        // If we aren't provided with a radius on one axis, use the
-        // information from the other axis.
-        radius_x(radius_x > 0 ? radius_x : radius_y),
-        radius_y(radius_y > 0 ? radius_y : radius_x),
-        force(force),
-        tilt_x(tilt_x),
-        tilt_y(tilt_y),
-        tangential_pressure(tangential_pressure),
-        twist(twist) {}
-  PointerDetails(EventPointerType pointer_type, const gfx::Vector2d& offset)
-      : pointer_type(pointer_type),
-        force(std::numeric_limits<float>::quiet_NaN()),
-        offset(offset) {}
+                 int twist = 0,
+                 uint32_t id = 0);
+  PointerDetails(EventPointerType pointer_type, const gfx::Vector2d& offset);
+  PointerDetails(const PointerDetails& other);
 
   bool operator==(const PointerDetails& other) const {
     return pointer_type == other.pointer_type && radius_x == other.radius_x &&
@@ -442,7 +429,7 @@ struct EVENTS_EXPORT PointerDetails {
             (std::isnan(force) && std::isnan(other.force))) &&
            tilt_x == other.tilt_x && tilt_y == other.tilt_y &&
            tangential_pressure == other.tangential_pressure &&
-           twist == other.twist && offset == other.offset;
+           twist == other.twist && id == other.id && offset == other.offset;
   }
 
   // The type of pointer device.
@@ -474,6 +461,9 @@ struct EVENTS_EXPORT PointerDetails {
   // degrees in the range [0,359]. Always 0 if the device does not support it.
   int twist = 0;
 
+  // An identifier that uniquely identifies a pointer during its lifetime.
+  uint32_t id = 0;

[mustaq, 2017/01/31 00:24:13]

Where do we set the id from lower level events? Do you think we need to fix
events_win.cc::GetMousePointerDetailsFromNative()? We seem to have a TODO there.

+

[sadrul, 2017/01/31 17:05:13]

ui::TouchEvent has a touch_id(), and a unique_event_id(). It also has a
PointerDetails, which now also has a id(). How are they related? Can we remove
one of the ids from TouchEvent?

ditto for ui::PointerEvent.

[lanwei, 2017/02/01 02:58:12]

This id in PointerDetails makes more senses for stylus type, because we will get
an ID from lower level events from the OS. For touch event, this id will be just
0, and eventually in Blink, the pointer id will be set by the touch_id() from
ui::TouchEvent. I guess we can use get rid of touch_id(), if we will use this
id. Dave, Mustaq, what do you think?

[sadrul, 2017/02/01 20:59:39]

Replacing TouchEvent::touch_id() (and I guess PointerEvent::pointer_id() too)
with this new *Event::PointerDetails::id() sounds reasonable to me.

   // 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.