Add support for field trial group to relax missing via header bypass logic.

components/data_reduction_proxy/core/browser/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 static_library("browser") {
   sources = [
     "data_reduction_proxy_auth_request_handler.cc",
     "data_reduction_proxy_auth_request_handler.h",
+    "data_reduction_proxy_bypass_protocol.cc",
+    "data_reduction_proxy_bypass_protocol.h",
     "data_reduction_proxy_configurator.cc",
     "data_reduction_proxy_configurator.h",
     "data_reduction_proxy_delegate.cc",
     "data_reduction_proxy_delegate.h",
     "data_reduction_proxy_interceptor.cc",
     "data_reduction_proxy_interceptor.h",
     "data_reduction_proxy_metrics.cc",
     "data_reduction_proxy_metrics.h",
     "data_reduction_proxy_network_delegate.cc",
     "data_reduction_proxy_network_delegate.h",
     "data_reduction_proxy_prefs.cc",
     "data_reduction_proxy_prefs.h",
-    "data_reduction_proxy_protocol.cc",
-    "data_reduction_proxy_protocol.h",
     "data_reduction_proxy_settings.cc",
     "data_reduction_proxy_settings.h",
     "data_reduction_proxy_statistics_prefs.cc",
     "data_reduction_proxy_statistics_prefs.h",
     "data_reduction_proxy_tamper_detection.cc",
     "data_reduction_proxy_tamper_detection.h",
     "data_reduction_proxy_usage_stats.cc",
     "data_reduction_proxy_usage_stats.h",
   ]
 
@@ skipping 30 matching lines @@
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "data_reduction_proxy_auth_request_handler_unittest.cc",
+    "data_reduction_proxy_bypass_protocol_unittest.cc",
     "data_reduction_proxy_configurator_unittest.cc",
     "data_reduction_proxy_interceptor_unittest.cc",
     "data_reduction_proxy_metrics_unittest.cc",
     "data_reduction_proxy_network_delegate_unittest.cc",
     "data_reduction_proxy_prefs_unittest.cc",
-    "data_reduction_proxy_protocol_unittest.cc",
     "data_reduction_proxy_settings_unittest.cc",
     "data_reduction_proxy_usage_stats_unittest.cc",
   ]
 
   deps = [
     ":browser",
     ":test_support",
     "//base",
     "//base:prefs_test_support",
     "//base/test:test_support",
     "//components/data_reduction_proxy/core/common:test_support",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }