Factor DRP PreviewsState logic out of content

components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc

 // 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.
 
 #include "components/data_reduction_proxy/core/common/data_reduction_proxy_headers.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <string>
@@ skipping 166 matching lines @@
 }
 
 const char* lite_page_directive() {
   return kLitePageDirective;
 }
 
 const char* compressed_video_directive() {
   return kCompressedVideoDirective;
 }
 
+const char* page_policies_directive() {
+  return kChromeProxyPagePoliciesDirective;
+}
+
 const char* chrome_proxy_experiment_force_lite_page() {
   return kChromeProxyExperimentForceLitePage;
 }
 
 const char* chrome_proxy_experiment_force_empty_image() {
   return kChromeProxyExperimentForceEmptyImage;
 }
 
 const char* if_heavy_qualifier() {
   return kIfHeavyQualifier;
@@ skipping 317 matching lines @@
   std::string value;
   size_t iter = 0;
   while (headers->EnumerateHeader(&iter, kChromeProxyHeader, &value)) {
     if (StartsWithActionPrefix(value, kChromeProxyActionFingerprintChromeProxy))
       continue;
     values->push_back(std::move(value));
   }
 }
 
 }  // namespace data_reduction_proxy