Adds button to VRShell menu mode, which lets the user manually exit WebVR presentation.

chrome/browser/android/vr_shell/vr_shell.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_ANDROID_VR_SHELL_VR_SHELL_H_
 #define CHROME_BROWSER_ANDROID_VR_SHELL_VR_SHELL_H_
 
 #include <jni.h>
 
 #include <memory>
@@ skipping 48 matching lines @@
   RELOAD,
   ZOOM_OUT,
   ZOOM_IN,
   RELOAD_UI,
   LOAD_URL,
   OMNIBOX_CONTENT,
   SET_CONTENT_PAUSED,
   SHOW_TAB,
   OPEN_NEW_TAB,
   KEY_EVENT,
+  EXIT_PRESENT,
 };
 
 class VrMetricsHelper;
 
 // The native instance of the Java VrShell. This class is not threadsafe and
 // must only be used on the UI thread.
 class VrShell : public device::GvrDelegate,
                 content::WebContentsObserver,
                 device::GvrGamepadDataProvider {
  public:
@@ skipping 185 matching lines @@
   base::WeakPtrFactory<VrShell> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VrShell);
 };
 
 bool RegisterVrShell(JNIEnv* env);
 
 }  // namespace vr_shell
 
 #endif  // CHROME_BROWSER_ANDROID_VR_SHELL_VR_SHELL_H_