VR: Add a native UI element scene manager

chrome/browser/android/vr_shell/BUILD.gn

Index: chrome/browser/android/vr_shell/BUILD.gn
diff --git a/chrome/browser/android/vr_shell/BUILD.gn b/chrome/browser/android/vr_shell/BUILD.gn
index 52c68dd76ca0545f3e8085a77b45df4cd7362dd4..7c978c14f1747be5a72c2d9e5da2ad0699fe5ba1 100644
--- a/chrome/browser/android/vr_shell/BUILD.gn
+++ b/chrome/browser/android/vr_shell/BUILD.gn
@@ -34,6 +34,8 @@ if (current_cpu == "arm" || current_cpu == "arm64") {
       "ui_interface.h",
       "ui_scene.cc",
       "ui_scene.h",
+      "ui_scene_manager.cc",
+      "ui_scene_manager.h",
       "vr_compositor.cc",
       "vr_compositor.h",
       "vr_controller.cc",
@@ -128,9 +130,8 @@ if (enable_vr) {
 
     # Ensure libgvr static library appears before gcc library in linking order.
     # See https://crbug.com/704305 for details.
-    libs = [
-      "//third_party/gvr-android-sdk/libgvr_shim_static_${current_cpu}.a",
-    ]
+    libs =
+        [ "//third_party/gvr-android-sdk/libgvr_shim_static_${current_cpu}.a" ]
 
     data = [
       "test/data/sample_inline.gltf",