Factor DRP PreviewsState logic out of content

components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc

Index: components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
diff --git a/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc b/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
index ef1e77faa3d285d7bf8659c86e794643d9dfe712..dd6dcee0abadea9186e7426c413f5b3b36c97110 100644
--- a/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
+++ b/components/data_reduction_proxy/core/common/data_reduction_proxy_headers.cc
@@ -43,6 +43,7 @@ const char kActionValueDelimiter = '=';
 const char kEmptyImageDirective[] = "empty-image";
 const char kLitePageDirective[] = "lite-page";
 const char kCompressedVideoDirective[] = "compressed-video";
+const char kChromeProxyPagePoliciesDirective[] = "page-policies";
 
 // The legacy Chrome-Proxy response header directive for LoFi images.
 const char kLegacyChromeProxyLoFiResponseDirective[] = "q=low";
@@ -157,6 +158,10 @@ const char* compressed_video_directive() {
   return kCompressedVideoDirective;
 }
 
+const char* page_policies_directive() {
+  return kChromeProxyPagePoliciesDirective;
+}
+
 const char* chrome_proxy_experiment_force_lite_page() {
   return kChromeProxyExperimentForceLitePage;
 }