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

chrome/browser/android/vr_shell/vr_shell.cc

 // 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.
 
 #include "chrome/browser/android/vr_shell/vr_shell.h"
 
 #include <android/native_window_jni.h>
 
 #include <string>
 #include <utility>
@@ skipping 472 matching lines @@
     case ZOOM_IN:   // Not handled yet.
       return;
     case KEY_EVENT: {
       int char_value;
       int modifiers = 0;
       arguments->GetInteger("modifiers", &modifiers);
       CHECK(arguments->GetInteger("charValue", &char_value));
       ui_input_manager_->GenerateKeyboardEvent(char_value, modifiers);
       return;
     }
+    case EXIT_PRESENT:
+      delegate_provider_->ExitWebVRPresent();
+      return;
 #if defined(ENABLE_VR_SHELL_UI_DEV)
     case RELOAD_UI:
       ui_contents_->GetController().Reload(content::ReloadType::NORMAL, false);
       html_interface_.reset(new UiInterface(UiInterface::Mode::STANDARD));
       SetUiState();
       vr_web_contents_observer_->SetUiInterface(html_interface_.get());
       return;
 #endif
     default:
       break;
@@ skipping 276 matching lines @@
            jboolean reprojected_rendering) {
   return reinterpret_cast<intptr_t>(new VrShell(
       env, obj, reinterpret_cast<ui::WindowAndroid*>(content_window_android),
       content::WebContents::FromJavaWebContents(ui_web_contents),
       reinterpret_cast<ui::WindowAndroid*>(ui_window_android), for_web_vr,
       VrShellDelegate::GetNativeVrShellDelegate(env, delegate),
       reinterpret_cast<gvr_context*>(gvr_api), reprojected_rendering));
 }
 
 }  // namespace vr_shell