Pause drawing webvr when the App button is pressed

chrome/browser/android/vr_shell/vr_thread_envoy.h

Index: chrome/browser/android/vr_shell/vr_thread_envoy.h
diff --git a/chrome/browser/android/vr_shell/vr_thread_envoy.h b/chrome/browser/android/vr_shell/vr_thread_envoy.h
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+// Copyright 2017 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_THREAD_ENVOY_H_
+#define CHROME_BROWSER_ANDROID_VR_SHELL_VR_THREAD_ENVOY_H_
+
+#include <memory>
+
+#include "base/bind.h"
+#include "base/memory/weak_ptr.h"
+#include "base/time/time.h"
+
+namespace vr_shell {
+
+class VrShell;
+
+// Interface for communication between the main and gl threads.
+class VrThreadEnvoy {
+ public:
+  virtual ~VrThreadEnvoy() {}
+
+  // Posts a task to call the given function with the given args on the main
+  // thread.
+  template <typename Functor, typename... Args>
+  void PostTaskToMainThread(Functor&& functor, Args&&... args) {
+    // We use PostDelayedTask insted of PostTask to make testing easier.
+    // PostTask is not virtual so test subclasses can't override it.
+    GetMainThreadTaskRunner()->PostDelayedTask(
+        FROM_HERE,
+        base::Bind(std::forward<Functor>(functor), std::forward<Args>(args)...),
+        base::TimeDelta());
+  }
+
+  // Same as PostTaskToMainThread but functor is expected to be a member
+  // function of VrShell.
+  template <typename Functor, typename... Args>
+  void PostTaskToMainThreadShell(Functor&& functor, Args&&... args) {
+    PostTaskToMainThread(std::forward<Functor>(functor), GetVrShell(),
+                         std::forward<Args>(args)...);
+  }
+
+ private:
+  virtual base::WeakPtr<VrShell> GetVrShell() = 0;
+  virtual scoped_refptr<base::SingleThreadTaskRunner>
+  GetMainThreadTaskRunner() = 0;
+};
+
+}  // namespace vr_shell
+
+#endif  // CHROME_BROWSER_ANDROID_VR_SHELL_VR_THREAD_ENVOY_H_