Don't deref ChildThread::current() when null (it can be null in some tests)

content/renderer/render_frame_impl.cc

Index: content/renderer/render_frame_impl.cc
diff --git a/content/renderer/render_frame_impl.cc b/content/renderer/render_frame_impl.cc
index 2141f47944ee52b0a6335879a24630103e78ca7f..7c90b7ae31a9319717db6e9cb93b07261ab8362c 100644
--- a/content/renderer/render_frame_impl.cc
+++ b/content/renderer/render_frame_impl.cc
@@ -1377,6 +1377,8 @@ blink::WebServiceWorkerProvider* RenderFrameImpl::createServiceWorkerProvider(
   DCHECK(!frame_ || frame_ == frame);
   // At this point we should have non-null data source.
   DCHECK(frame->dataSource());
+  if (!ChildThread::current())
+    return NULL;  // May be null in some tests.
   ServiceWorkerNetworkProvider* provider =
       ServiceWorkerNetworkProvider::FromDocumentState(
           DocumentState::FromDataSource(frame->dataSource()));