Separate motion event touch geometry orientation from stylus orientation.

content/browser/renderer_host/input/motion_event_android.cc

Index: content/browser/renderer_host/input/motion_event_android.cc
diff --git a/content/browser/renderer_host/input/motion_event_android.cc b/content/browser/renderer_host/input/motion_event_android.cc
index 8d36c812cc0084dc9ba3d5cb2d9fa0459ff23832..15a2aca39c547d4dac1f3f12742db61450dcaf57 100644
--- a/content/browser/renderer_host/input/motion_event_android.cc
+++ b/content/browser/renderer_host/input/motion_event_android.cc
@@ -258,6 +258,21 @@ float MotionEventAndroid::GetOrientation(size_t pointer_index) const {
       AttachCurrentThread(), event_.obj(), pointer_index));
 }
 
+float MotionEventAndroid::GetTouchOrientation(size_t pointer_index) const {
+  float orientation = GetOrientation(pointer_index);
+  // The meaning of the motion event orientation is overloaded on Android.
+  // * For a touch screen or pad, it's the orientation of the touch major axis
+  //   clockwise from vertical. The value lies in [-PI/1, PI/2].
+  // * For a stylus, it indicates the direction in which the stylus is pointing
+  //   clockwise from top. The value lies in [-PI, PI].
+  // Map to touch major axis orientation.
+  if (orientation <= -M_PI_2)
+    return orientation + M_PI;
+  if (orientation >= M_PI_2)
+    return orientation - M_PI;
+  return orientation;
+}
+
 float MotionEventAndroid::GetPressure(size_t pointer_index) const {
   DCHECK_LT(pointer_index, cached_pointer_count_);
   // Note that this early return is a special case exercised only in testing, as