Fix motion event orientation handling for styluses.

ui/events/gesture_detection/motion_event.h

 // Copyright 2014 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_GESTURE_DETECTION_MOTION_EVENT_H_
 #define UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "ui/events/gesture_detection/gesture_detection_export.h"
@@ skipping 74 matching lines @@
   float GetX() const { return GetX(0); }
   float GetY() const { return GetY(0); }
   float GetRawX() const { return GetRawX(0); }
   float GetRawY() const { return GetRawY(0); }
   float GetRawOffsetX() const { return GetRawX() - GetX(); }
   float GetRawOffsetY() const { return GetRawY() - GetY(); }
 
   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); }
   ToolType GetToolType() const { return GetToolType(0); }
 
   // O(N) search of pointers (use sparingly!). Returns -1 if |id| nonexistent.
   int FindPointerIndexOfId(int id) const;
 
   // Note that these methods perform shallow copies of the originating events.
   // They guarantee only that the returned type will reflect the same
   // data exposed by the MotionEvent interface; no guarantees are made that the
   // underlying implementation is identical to the source implementation.
   scoped_ptr<MotionEvent> Clone() const;
   scoped_ptr<MotionEvent> Cancel() const;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_MOTION_EVENT_H_