Let HTML UI manage menu mode.

chrome/browser/android/vr_shell/vr_shell.h

Index: chrome/browser/android/vr_shell/vr_shell.h
diff --git a/chrome/browser/android/vr_shell/vr_shell.h b/chrome/browser/android/vr_shell/vr_shell.h
index 54f84d009bba0f9ebfdcd2a24168215295e44a4f..81c0ed93a506f108f34cc22ca34ea0ce49e6fb75 100644
--- a/chrome/browser/android/vr_shell/vr_shell.h
+++ b/chrome/browser/android/vr_shell/vr_shell.h
@@ -55,6 +55,7 @@ enum UiAction {
   RELOAD_UI,
   LOAD_URL,
   OMNIBOX_CONTENT,
+  SET_CONTENT_PAUSED,
 };
 
 class VrMetricsHelper;
@@ -156,6 +157,7 @@ class VrShell : public device::GvrDelegate, content::WebContentsObserver {
  private:
   ~VrShell() override;
   void PostToGlThreadWhenReady(const base::Closure& task);
+  void SetContentPaused(bool paused);
 
   // content::WebContentsObserver implementation.
   void RenderViewHostChanged(content::RenderViewHost* old_host,
@@ -182,6 +184,8 @@ class VrShell : public device::GvrDelegate, content::WebContentsObserver {
   void ProcessTabArray(JNIEnv* env, jobjectArray tabs, bool incognito);
 
   std::unique_ptr<UiInterface> html_interface_;
+  bool content_paused_ = false;
+  bool webvr_mode_ = false;
 
   content::WebContents* main_contents_;
   std::unique_ptr<VrCompositor> content_compositor_;