Enable magic window mode with new Gvr

chrome/android/java/src/org/chromium/chrome/browser/vr_shell/NonPresentingGvrContextInterface.java

+// 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.
+
+package org.chromium.chrome.browser.vr_shell;
+
+/**
+ * Abstracts away the NonPresentingGvrContext class, which may or may not be present at runtime
+ * depending on compile flags.
+ */
+public interface NonPresentingGvrContextInterface {
+    /**
+     * Returns the native gvr context.
+     */
+    long getNativeGvrContext();
+
+    /**
+     * Must be called when activity resumes.
+     */
+    void resume();
+
+    /**
+     * Must be called when activity pauses.
+     */
+    void pause();
+
+    /**
+     * Shutdown the native gvr context.
+     */
+    void shutdown();
+}