Clean up threading around VR Scene updates.

chrome/browser/android/vr_shell/vr_shell_gl.cc

Index: chrome/browser/android/vr_shell/vr_shell_gl.cc
diff --git a/chrome/browser/android/vr_shell/vr_shell_gl.cc b/chrome/browser/android/vr_shell/vr_shell_gl.cc
index a2ac61588d22344527cf9a215cd35587f0e756c6..6799881daeeb32801cd582500274040985be0b59 100644
--- a/chrome/browser/android/vr_shell/vr_shell_gl.cc
+++ b/chrome/browser/android/vr_shell/vr_shell_gl.cc
@@ -169,6 +169,11 @@ int GetPixelEncodedPoseIndexByte() {
   return -1;
 }
 
+int64_t TimeInMicroseconds() {
+  return std::chrono::duration_cast<std::chrono::microseconds>(
+      std::chrono::steady_clock::now().time_since_epoch()).count();
+}
+
 }  // namespace
 
 VrShellGl::VrShellGl(
@@ -650,7 +655,7 @@ void VrShellGl::DrawFrame() {
 
   // Update the render position of all UI elements (including desktop).
   const float screen_tilt = kDesktopScreenTiltDefault * M_PI / 180.0f;
-  scene_->UpdateTransforms(screen_tilt, UiScene::TimeInMicroseconds());
+  scene_->UpdateTransforms(screen_tilt, TimeInMicroseconds());
 
   UpdateController(GetForwardVector(head_pose));
 
@@ -1010,4 +1015,8 @@ void VrShellGl::ForceExitVR() {
       FROM_HERE, base::Bind(&VrShell::ForceExitVR, weak_vr_shell_));
 }
 
+void VrShellGl::UpdateScene(std::unique_ptr<base::ListValue> commands) {
+  scene_->HandleCommands(std::move(commands), TimeInMicroseconds());
+}
+
 }  // namespace vr_shell