Add Mojo API for Blink hit testing

services/viz/public/interfaces/hit_test/input_hit_test.mojom

Index: services/viz/public/interfaces/hit_test/input_hit_test.mojom
diff --git a/services/viz/public/interfaces/hit_test/input_hit_test.mojom b/services/viz/public/interfaces/hit_test/input_hit_test.mojom
new file mode 100644
index 0000000000000000000000000000000000000000..10b758dfd7959d882a5a8857f9930d59a41fe21b
--- /dev/null
+++ b/services/viz/public/interfaces/hit_test/input_hit_test.mojom
@@ -0,0 +1,8 @@
+module viz.mojom;

[Navid Zolghadr, 2017/08/09 16:08:22]

Is this place alright for the mojom file?

[rjkroege, 2017/08/14 18:26:58]

We discussed collectively. In the short term, having this here is (reluctantly)
acceptable but in the fullness of time when all Chrome implementations use the
services/ui window server (i.e. mus), the interface should get relocated to
services/ui/public/

The reasoning behind this is that this interface is part (or associated with)
the WindowTreeClient interface. In a  mus context, a client would specify this
interface via its WindowTree interface (exact plumbing to be worked out over
time.)

So: please add an appropriate TODO

[Navid Zolghadr, 2017/08/18 15:29:48]

Done.

+
+import "ui/gfx/geometry/mojo/geometry.mojom";
+  
+// Returns the hit-tested remote frame id for the given coordinates.
+interface FrameInputHitTest {

[rjkroege, 2017/08/14 18:26:58]

I am opposed to this name. The "Test" suffix suggests test code. I called this
"immediate" mode in the initial design doc but it's actually a delegate pattern
so I'm going to suggest calling this something like TargetFrameForInputDelegate
(and file name should match.)

[Navid Zolghadr, 2017/08/18 15:29:48]

Done.

+  HitTestFrameAt(gfx.mojom.Point point) => (int32 frame_id);
+};