Fix motion event orientation handling for styluses.

ui/events/gesture_detection/motion_event.h

Index: ui/events/gesture_detection/motion_event.h
diff --git a/ui/events/gesture_detection/motion_event.h b/ui/events/gesture_detection/motion_event.h
index a6028fbdee52c3feb6394960f08ae0b563119270..12834a793f2db1e51e2af8a621fb98c139bdb32c 100644
--- a/ui/events/gesture_detection/motion_event.h
+++ b/ui/events/gesture_detection/motion_event.h
@@ -92,8 +92,11 @@ class GESTURE_DETECTION_EXPORT MotionEvent {
   float GetTouchMajor() const { return GetTouchMajor(0); }
   float GetTouchMinor() const { return GetTouchMinor(0); }
 
-  // Returns the orientation of the major axis clockwise from vertical, in
-  // radians. The return value lies in [-PI/2, PI/2].
+  // Returns the orientation in radians. The meaning is overloaded:
+  // * For a touch screen or pad, it's the orientation of the major axis
+  //   clockwise from vertical. The return value lies in [-PI/2, PI/2].
+  // * For a stylus, it indicates the direction in which the stylus is pointing.
+  //   The return value lies in [-PI, PI].
   float GetOrientation() const { return GetOrientation(0); }
 
   float GetPressure() const { return GetPressure(0); }