Exit VR when our main content tab is hidden (Usually due to links opening in new tab)

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 77 matching lines @@
   void DrawFrame(JNIEnv* env, const base::android::JavaParamRef<jobject>& obj);
   void OnTriggerEvent(JNIEnv* env,
                       const base::android::JavaParamRef<jobject>& obj);
   void OnPause(JNIEnv* env, const base::android::JavaParamRef<jobject>& obj);
   void OnResume(JNIEnv* env, const base::android::JavaParamRef<jobject>& obj);
   void SetWebVrMode(JNIEnv* env,
                     const base::android::JavaParamRef<jobject>& obj,
                     bool enabled);
 
   void ContentWebContentsDestroyed();
+  // Called when our WebContents have been hidden. Usually a sign that something
+  // like another tab placed in front of it.
+  void ContentWasHidden();
 
   // html/js UI hooks.
   static base::WeakPtr<VrShell> GetWeakPtr(
       const content::WebContents* web_contents);
   UiScene* GetScene();
   UiInterface* GetUiInterface();
   void OnDomContentsLoaded();
 
   // device::GvrDelegate implementation
   void SetWebVRSecureOrigin(bool secure_origin) override;
@@ skipping 131 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_