Do not attempt to use data reduction proxy when holdback is enabled

components/data_reduction_proxy/core/browser/data_reduction_proxy_delegate_unittest.cc

Index: components/data_reduction_proxy/core/browser/data_reduction_proxy_delegate_unittest.cc
diff --git a/components/data_reduction_proxy/core/browser/data_reduction_proxy_delegate_unittest.cc b/components/data_reduction_proxy/core/browser/data_reduction_proxy_delegate_unittest.cc
index 462c92b0f652bb0540dd2b7eaf8977d69b6e9f16..5c4f2c15a4a6e9e4a3ae02c7cd3beb79070d1b22 100644
--- a/components/data_reduction_proxy/core/browser/data_reduction_proxy_delegate_unittest.cc
+++ b/components/data_reduction_proxy/core/browser/data_reduction_proxy_delegate_unittest.cc
@@ -860,6 +860,36 @@ TEST_F(DataReductionProxyDelegateTest, TimeToFirstHttpDataSaverRequest) {
   }
 }
 
+TEST_F(DataReductionProxyDelegateTest, Holdback) {
+  const char kResponseHeaders[] =
+      "HTTP/1.1 200 OK\r\n"
+      "Via: 1.1 Chrome-Compression-Proxy-Suffix\r\n"
+      "Content-Length: 10\r\n\r\n";
+
+  const struct {
+    bool holdback;
+  } tests[] = {
+      {
+          true,
+      },
+      {
+          false,
+      },
+  };
+  for (const auto& test : tests) {
+    base::FieldTrialList field_trial_list(nullptr);
+    ASSERT_TRUE(base::FieldTrialList::CreateFieldTrial(
+        "DataCompressionProxyHoldback", test.holdback ? "Enabled" : "Control"));
+
+    base::HistogramTester histogram_tester;
+    FetchURLRequest(GURL("http://example.com/path/"), nullptr, kResponseHeaders,
+                    10);
+    histogram_tester.ExpectTotalCount(
+        "DataReductionProxy.SuccessfulRequestCompletionCounts",
+        test.holdback ? 0 : 1);
+  }
+}
+
 TEST_F(DataReductionProxyDelegateTest, OnCompletedSizeFor304) {
   int64_t baseline_received_bytes = total_received_bytes();
   int64_t baseline_original_received_bytes = total_original_received_bytes();