Fix the flaky Warmup URL test in data reduction proxy

components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
index afcbb44bdb433ad56442d07b51ef0bee8f9ed276..9ffb7f87fd125f7f521b0c079468e604cc0250cb 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_config.cc
@@ -312,20 +312,12 @@ class WarmupURLFetcher : public net::URLFetcherDelegate {
     fetcher_->Start();
   }
 
-  void SetWarmupURLFetcherCallbackForTesting(
-      base::Callback<void()> warmup_url_fetched_callback) {
-    fetch_completion_callback_ = warmup_url_fetched_callback;
-  }
-
  private:
   void OnURLFetchComplete(const net::URLFetcher* source) override {
     DCHECK_EQ(source, fetcher_.get());
     UMA_HISTOGRAM_BOOLEAN(
         "DataReductionProxy.WarmupURL.FetchSuccessful",
         source->GetStatus().status() == net::URLRequestStatus::SUCCESS);
-
-    if (fetch_completion_callback_)
-      fetch_completion_callback_.Run();
   }
 
   scoped_refptr<net::URLRequestContextGetter> url_request_context_getter_;
@@ -333,9 +325,6 @@ class WarmupURLFetcher : public net::URLFetcherDelegate {
   // The URLFetcher being used for fetching the warmup URL.
   std::unique_ptr<net::URLFetcher> fetcher_;
 
-  // Called upon the completion of fetching of the warmup URL. May be null.
-  base::Callback<void()> fetch_completion_callback_;
-
   DISALLOW_COPY_AND_ASSIGN(WarmupURLFetcher);
 };
 
@@ -871,14 +860,6 @@ void DataReductionProxyConfig::FetchWarmupURL() {
   warmup_url_fetcher_->FetchWarmupURL();
 }
 
-void DataReductionProxyConfig::SetWarmupURLFetcherCallbackForTesting(
-    base::Callback<void()> warmup_url_fetched_callback) {
-  DCHECK(thread_checker_.CalledOnValidThread());
-
-  warmup_url_fetcher_->SetWarmupURLFetcherCallbackForTesting(
-      warmup_url_fetched_callback);
-}
-
 void DataReductionProxyConfig::SetLoFiModeOff() {
   DCHECK(thread_checker_.CalledOnValidThread());
   lofi_off_ = true;