Adds NULL checks in RenderFrameHostImpl::GetVisibilityState().

content/browser/frame_host/render_frame_host_impl.cc

 // Copyright 2013 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/frame_host/render_frame_host_impl.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/containers/hash_tables.h"
 #include "base/lazy_instance.h"
@@ skipping 360 matching lines @@
 
 RenderViewHost* RenderFrameHostImpl::GetRenderViewHost() {
   return render_view_host_;
 }
 
 ServiceRegistry* RenderFrameHostImpl::GetServiceRegistry() {
   return service_registry_.get();
 }
 
 blink::WebPageVisibilityState RenderFrameHostImpl::GetVisibilityState() {
+  // Works around the crashes seen in https://crbug.com/501863, where the
+  // active WebContents from a browser iterator may contain a render frame
+  // detached from the frame tree.
+  RenderWidgetHostView* view = RenderFrameHostImpl::GetView();
+  if (!view || !view->GetRenderWidgetHost())
+    return blink::WebPageVisibilityStateHidden;
+
   // TODO(mlamouri,kenrb): call GetRenderWidgetHost() directly when it stops
   // returning nullptr in some cases. See https://crbug.com/455245.
   blink::WebPageVisibilityState visibility_state =
-      RenderWidgetHostImpl::From(GetView()->GetRenderWidgetHost())->is_hidden()
+      RenderWidgetHostImpl::From(view->GetRenderWidgetHost())->is_hidden()
           ? blink::WebPageVisibilityStateHidden
           : blink::WebPageVisibilityStateVisible;
   GetContentClient()->browser()->OverridePageVisibilityState(this,
                                                              &visibility_state);
   return visibility_state;
 }
 
 bool RenderFrameHostImpl::Send(IPC::Message* message) {
   if (IPC_MESSAGE_ID_CLASS(message->type()) == InputMsgStart) {
     return render_view_host_->input_router()->SendInput(
@@ skipping 1847 matching lines @@
             BrowserPluginInstanceIDToAXTreeID(value)));
         break;
       case AX_CONTENT_INT_ATTRIBUTE_LAST:
         NOTREACHED();
         break;
     }
   }
 }
 
 }  // namespace content