VR: Fix injected hover events for web contents

Injecting HOVER_EXIT is done by the platform if the coordinates for the
HOVER_MOVE are out of bounds, so we don't need to inject it ourself.

Bug: 819348
Change-Id: I4486f9970fac031373215bdcb7021de6a422da02
Reviewed-on: https://chromium-review.googlesource.com/1014715Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Yash Malik <ymalik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551375}

chrome/browser/android/vr/android_ui_gesture_target.cc

@@ -93,12 +93,11 @@ void AndroidUiGestureTarget::DispatchWebInputEvent(
       Inject(content::MOTION_EVENT_ACTION_HOVER_ENTER, event_time_ms);
       break;
     case blink::WebMouseEvent::kMouseMove:
-      SetPointer(mouse->PositionInWidget().x, mouse->PositionInWidget().y);
-      Inject(content::MOTION_EVENT_ACTION_HOVER_MOVE, event_time_ms);
-      break;
     case blink::WebMouseEvent::kMouseLeave:
+      // We don't need to inject MOTION_EVENT_ACTION_HOVER_EXIT as the platform
+      // will generate it for us if the pointer is out of bounds.
       SetPointer(mouse->PositionInWidget().x, mouse->PositionInWidget().y);
-      Inject(content::MOTION_EVENT_ACTION_HOVER_EXIT, event_time_ms);
+      Inject(content::MOTION_EVENT_ACTION_HOVER_MOVE, event_time_ms);
       break;
     case blink::WebMouseEvent::kMouseDown:
       // Mouse down events are translated into touch events on Android anyways,