App button click exits WebVR presentation.

chrome/browser/android/vr_shell/vr_gl_thread.cc

Index: chrome/browser/android/vr_shell/vr_gl_thread.cc
diff --git a/chrome/browser/android/vr_shell/vr_gl_thread.cc b/chrome/browser/android/vr_shell/vr_gl_thread.cc
index 0fc3ea0e6782a83f2e5fa46dea755c9945b9bae9..03839d61abcd24f7d86110ed7e7f87ddfda878ba 100644
--- a/chrome/browser/android/vr_shell/vr_gl_thread.cc
+++ b/chrome/browser/android/vr_shell/vr_gl_thread.cc
@@ -83,6 +83,11 @@ void VrGLThread::ForceExitVr() {
       FROM_HERE, base::Bind(&VrShell::ForceExitVr, weak_vr_shell_));
 }
 
+void VrGLThread::ExitPresent() {
+  main_thread_task_runner_->PostTask(
+      FROM_HERE, base::Bind(&VrShell::ExitPresent, weak_vr_shell_));
+}
+
 void VrGLThread::RunVRDisplayInfoCallback(
     const base::Callback<void(device::mojom::VRDisplayInfoPtr)>& callback,
     device::mojom::VRDisplayInfoPtr* info) {