Fix motion event orientation handling for styluses.

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 9a3a648ae3306e5517b87255acd1c5d0f1fac847..47ed7873c763e6f3754e7c8e90312e0dc7b905c8 100644
--- a/ui/events/blink/blink_event_util.cc
+++ b/ui/events/blink/blink_event_util.cc
@@ -103,9 +103,15 @@ WebTouchPoint CreateWebTouchPoint(const MotionEvent& event,
   DCHECK_GE(major_radius, 0);
   DCHECK_GE(minor_radius, 0);
   DCHECK_GE(major_radius, minor_radius);
+  // Orientation lies in [-90, 90] for a touch screen or pad and in [-180, 180]
+  // for a stylus.
   // Allow a small bound tolerance to account for floating point conversion.
-  DCHECK_GT(orientation_deg, -90.01f);
-  DCHECK_LT(orientation_deg, 90.01f);
+  DCHECK_GT(orientation_deg, -180.01f);
+  DCHECK_LT(orientation_deg, 180.01f);
+  if (orientation_deg >= 90.f)

[sky, 2015/05/26 19:51:04]

Why do you need to do this and 113?

[Rick Byers, 2015/05/26 20:21:33]

Presumably because the TouchEvent extensions note says TouchEvent.rotationAngle
is always between 0 and 90:
https://dvcs.w3.org/hg/webevents/raw-file/default/touchevents.html#widl-Touch....
 This is because rotationAngle is designed to be about contact geometry, not
tool rotation.  Personally I think it was a mistake for Android to re-use the
same API for these conceptually different scenarios.

Fixing this up so we conform to the spec LGTM, thanks!

[mustaq, 2015/05/26 21:25:59]

I agree with Rick that using "orientation" to represent two different concepts
in Android MotionEvent spec was a mistake. And I think we should not carry over
the same mistake here, for two reasons:

- TouchEvent rotationAngle stirctly represents touch geometry, so using this
field to represent stylus orientation is like expanding the scope of the Android
mistake.

- For stylus, forcing the orientation to within +-90 degrees is wrong. For
example, +135 degrees means the stylus is pointing downward-right, and fixing it
to +135-180 = -45 degrees means it is now pointing upward-left.

+    orientation_deg -= 180.f;
+  if (orientation_deg <= -90.f)
+    orientation_deg += 180.f;
   if (orientation_deg >= 0) {
     // The case orientation_deg == 0 is handled here on purpose: although the
     // 'else' block is equivalent in this case, we want to pass the 0 value