Fix PointerLockBrowserTest on Mac.

content/browser/pointer_lock_browsertest_mac.mm

 // 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.
 
 #include "content/browser/pointer_lock_browsertest.h"
 
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_view_mac.h"
 #include "content/browser/web_contents/web_contents_view_mac.h"
 
 namespace content {
 
 namespace {
 
 class MockRenderWidgetHostView : public RenderWidgetHostViewMac {
  public:
   MockRenderWidgetHostView(RenderWidgetHost* host, bool is_guest_view_hack)
-      : RenderWidgetHostViewMac(host, is_guest_view_hack),
-        host_(RenderWidgetHostImpl::From(host)) {}
+      : RenderWidgetHostViewMac(host, is_guest_view_hack) {}
   ~MockRenderWidgetHostView() override {
     if (mouse_locked_)
       UnlockMouse();
   }
 
   bool LockMouse() override {
     mouse_locked_ = true;
 
     return true;
   }
 
   void UnlockMouse() override {
-    host_->LostMouseLock();
+    if (RenderWidgetHostImpl* host =
+            RenderWidgetHostImpl::From(GetRenderWidgetHost())) {
+      host->LostMouseLock();
+    }
     mouse_locked_ = false;
   }
 
   bool IsMouseLocked() override { return mouse_locked_; }
 
   bool HasFocus() const override { return true; }
-
-  RenderWidgetHostImpl* host_;
 };
 
 }  // namespace
 
 void InstallCreateHooksForPointerLockBrowserTests() {
   WebContentsViewMac::InstallCreateHookForTests(
       [](RenderWidgetHost* host,
          bool is_guest_view_hack) -> RenderWidgetHostViewMac* {
         return new MockRenderWidgetHostView(host, is_guest_view_hack);
       });
 }
 
 }  // namespace content