Remove the dependence on BrowserThread::FILE for

net/url_request/url_request_context_builder.cc

Index: net/url_request/url_request_context_builder.cc
diff --git a/net/url_request/url_request_context_builder.cc b/net/url_request/url_request_context_builder.cc
index a1e384d9886375985e156cb7eda5cea2c6b9a808..6d5e797f7dbdc5724938bf72530e90a48a4dd308 100644
--- a/net/url_request/url_request_context_builder.cc
+++ b/net/url_request/url_request_context_builder.cc
@@ -428,8 +428,7 @@ std::unique_ptr<URLRequestContext> URLRequestContextBuilder::Build() {
     // ProxyService::CreateSystemProxyConfigService()'s signature doesn't suck.
     if (!proxy_config_service_) {
       proxy_config_service_ = ProxyService::CreateSystemProxyConfigService(
-          base::ThreadTaskRunnerHandle::Get().get(),
-          context->GetFileTaskRunner());
+          base::ThreadTaskRunnerHandle::Get().get());
     }
 #endif  // !defined(OS_LINUX) && !defined(OS_ANDROID)
     proxy_service_ =