Check for the RWHIER being null when informing it of a child view detach

Bug: 914479
Change-Id: I874361216d1ae45fe0b0a7ef51d730ef895649b9
Reviewed-on: https://chromium-review.googlesource.com/c/1374519Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Kevin McNee <mcnee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616078}

content/browser/frame_host/cross_process_frame_connector.cc

@@ -119,7 +119,11 @@ void CrossProcessFrameConnector::SetView(RenderWidgetHostViewChildFrame* view) {
     // be called during nested WebContents destruction. See
     // https://crbug.com/644306.
     if (GetParentRenderWidgetHostView() &&
-        GetParentRenderWidgetHostView()->host()->delegate()) {
+        GetParentRenderWidgetHostView()->host()->delegate() &&
+        GetParentRenderWidgetHostView()
+            ->host()
+            ->delegate()
+            ->GetInputEventRouter()) {
       GetParentRenderWidgetHostView()
           ->host()
           ->delegate()