Fix a crash and a timeout issue.

WebXR may not submit frames if pose data is null.  Pose data will
be null if WebXR isn't visible.  However, we want at least one pose
data to be non-null to know that WebXR is ready to submit frames.

The fix is to hand out a non-null pose data.

Also, fix a crash.  graphics_ is set to null when UI hides, but we
may still have an outstanding frame callback.

Change-Id: Ib304a0b56d8737da1d8200cbb6257645755c99ba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1540616Reviewed-by: Klaus Weidner <klausw@chromium.org>
Commit-Queue: Bill Orr <billorr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644604}

chrome/browser/vr/win/vr_browser_renderer_thread_win.cc

@@ -293,7 +293,9 @@ void VRBrowserRendererThreadWin::OnPose(device::mojom::XRFrameDataPtr data) {
     // We shouldn't be showing UI.
     overlay_->SetOverlayAndWebXRVisibility(draw_state_.ShouldDrawUI(),
                                            draw_state_.ShouldDrawWebXR());
-    graphics_->ResetMemoryBuffer();
+
+    if (graphics_)
+      graphics_->ResetMemoryBuffer();
     return;
   }
 

device/vr/windows/compositor_base.cc

@@ -99,7 +99,6 @@ void XRCompositorCommon::SubmitFrameWithTextureHandle(
     int16_t frame_index,
     mojo::ScopedHandle texture_handle) {
   TRACE_EVENT1("xr", "SubmitFrameWithTextureHandle", "frameIndex", frame_index);
-
   webxr_has_pose_ = false;
   // Tell the browser that WebXR has submitted a frame.
   if (on_webxr_submitted_)
@@ -351,7 +350,8 @@ void XRCompositorCommon::GetControllerDataAndSendFrameData(
 
   // We have posted a message to allow other calls to get through, and now state
   // may have changed.  WebXR may not be presenting any more, or may be hidden.
-  std::move(callback).Run(is_presenting_ && webxr_visible_
+  std::move(callback).Run(is_presenting_ &&
+                                  (webxr_visible_ || on_webxr_submitted_)
                               ? std::move(frame_data)
                               : mojom::XRFrameData::New());
 }