Cleans up events to just the parts we're actually using

Also unifies mouse and touch into a single event type.

R=abarth@chromium.org, erg@chromium.org

Review URL: https://codereview.chromium.org/1033513003
diff --git a/examples/spinning_cube/spinning_cube_app.cc b/examples/spinning_cube/spinning_cube_app.cc
index a239496..1c8d145 100644
--- a/examples/spinning_cube/spinning_cube_app.cc
+++ b/examples/spinning_cube/spinning_cube_app.cc
@@ -62,7 +62,7 @@
   void OnEvent(mojo::EventPtr event,
                const mojo::Callback<void()>& callback) override {
     assert(event);
-    if (event->location_data && event->location_data->in_view_location)
+    if (event->pointer_data.get())
       gles2_client_->HandleInputEvent(*event);
     callback.Run();
   }