Reland of App button click exits WebVR presentation.

chrome/browser/android/vr_shell/vr_shell_delegate.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_delegate.h"
 
 #include <utility>
 
 #include "base/android/jni_android.h"
 #include "base/callback_helpers.h"
@@ skipping 173 matching lines @@
   // If/When VRShell is ready for use it will call SetPresentResult.
   JNIEnv* env = AttachCurrentThread();
   Java_VrShellDelegate_presentRequested(env, j_vr_shell_delegate_.obj());
 }
 
 void VrShellDelegate::ExitWebVRPresent() {
   // VRShell is no longer needed by WebVR, allow it to shut down if it's not
   // being used elsewhere.
   JNIEnv* env = AttachCurrentThread();
   if (Java_VrShellDelegate_exitWebVRPresent(env, j_vr_shell_delegate_.obj())) {
-    device_provider_->Device()->OnExitPresent();
+    if (device_provider_) {
+      device_provider_->Device()->OnExitPresent();
+    }
   }
 }
 
 void VrShellDelegate::CreateNonPresentingDelegate() {
   JNIEnv* env = AttachCurrentThread();
   gvr_context* context = reinterpret_cast<gvr_context*>(
       Java_VrShellDelegate_createNonPresentingNativeContext(
           env, j_vr_shell_delegate_.obj()));
   non_presenting_delegate_ =
       base::MakeUnique<NonPresentingGvrDelegate>(context);
@@ skipping 32 matching lines @@
 jlong Init(JNIEnv* env, const JavaParamRef<jobject>& obj) {
   return reinterpret_cast<intptr_t>(new VrShellDelegate(env, obj));
 }
 
 static void OnLibraryAvailable(JNIEnv* env, const JavaParamRef<jclass>& clazz) {
   device::GvrDelegateProvider::SetInstance(
       base::Bind(&VrShellDelegate::CreateVrShellDelegate));
 }
 
 }  // namespace vr_shell