Adds UMA to measure when the data reduction proxy via header is missing

components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detection_unittest.cc

Index: components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detection_unittest.cc
diff --git a/components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detection_unittest.cc b/components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detection_unittest.cc
index 6c28806d86afeb4aa2ce6d5b9bd0705d2d94cacc..6f487522f460b80a0fd9ccd3bde1d2a7d57b2cec 100644
--- a/components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detection_unittest.cc
+++ b/components/data_reduction_proxy/browser/data_reduction_proxy_tamper_detection_unittest.cc
@@ -15,6 +15,7 @@
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "components/data_reduction_proxy/common/data_reduction_proxy_headers.h"
+#include "components/data_reduction_proxy/common/data_reduction_proxy_headers_test_utils.h"
 #include "net/http/http_response_headers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -25,12 +26,6 @@
 
 namespace {
 
-void HeadersToRaw(std::string* headers) {
-  std::replace(headers->begin(), headers->end(), '\n', '\0');
-  if (!headers->empty())
-    *headers += '\0';
-}
-
 // Calcuates MD5 hash value for a string and then base64 encode it. Testcases
 // contain expected fingerprint in plain text, which needs to be encoded before
 // comparison.