Pass MotionEvent tilt angles to Blink on Android.

ui/events/blink/blink_event_util.cc

Index: ui/events/blink/blink_event_util.cc
diff --git a/ui/events/blink/blink_event_util.cc b/ui/events/blink/blink_event_util.cc
index 4dca563ae5c751413b40668f62c68a53b8eacde1..431c52560401b06a615a45764fcf876af2932eb7 100644
--- a/ui/events/blink/blink_event_util.cc
+++ b/ui/events/blink/blink_event_util.cc
@@ -125,7 +125,8 @@ WebTouchPoint CreateWebTouchPoint(const MotionEvent& event,
   DCHECK_LE(minor_radius, major_radius);
   DCHECK_IMPLIES(major_radius, minor_radius);
 
-  float orientation_deg = event.GetOrientation(pointer_index) * 180.f / M_PI;
+  float orientation_rad = event.GetOrientation(pointer_index);
+  float orientation_deg = orientation_rad * 180.f / M_PI;
   DCHECK_GE(major_radius, 0);
   DCHECK_GE(minor_radius, 0);
   DCHECK_GE(major_radius, minor_radius);
@@ -158,6 +159,18 @@ WebTouchPoint CreateWebTouchPoint(const MotionEvent& event,
 
   touch.force = event.GetPressure(pointer_index);
 
+  if (event.GetToolType(pointer_index) == MotionEvent::TOOL_TYPE_STYLUS) {
+    // A stylus points to a direction specified by orientation and tilts to
+    // the opposite direction. Coordinate system is left-handed.
+    float tilt_rad = event.GetTilt(pointer_index);
+    float r = sin(tilt_rad);
+    float z = cos(tilt_rad);
+    touch.tiltX = lround(atan2(sin(-orientation_rad) * r, z) * 180.f / M_PI);
+    touch.tiltY = lround(atan2(cos(-orientation_rad) * r, z) * 180.f / M_PI);
+  } else {
+    touch.tiltX = touch.tiltY = 0;
+  }
+
   return touch;
 }