Modify data_reduction_proxy_header to support tamper detection logic.

components/data_reduction_proxy/common/data_reduction_proxy_headers.h

Index: components/data_reduction_proxy/common/data_reduction_proxy_headers.h
diff --git a/components/data_reduction_proxy/common/data_reduction_proxy_headers.h b/components/data_reduction_proxy/common/data_reduction_proxy_headers.h
index c2ca1df5f15aafe4dec8622c0aedd127a0a1efe0..9fdb19015be0d7d0106b5ac1a6378bbb8cb0cf4e 100644
--- a/components/data_reduction_proxy/common/data_reduction_proxy_headers.h
+++ b/components/data_reduction_proxy/common/data_reduction_proxy_headers.h
@@ -51,6 +51,14 @@ GetDataReductionProxyBypassEventType(
     const net::HttpResponseHeaders* headers,
     DataReductionProxyInfo* proxy_info);
 
+// Searches for the specified Chrome-Proxy action, and if present saves its
+// value as a string in |action_value|. Only keeps the first one and ignores
+// the rest if multiple actions match |action_prefix|.
+bool GetDataReductionProxyActionValue(
+    const net::HttpResponseHeaders* headers,
+    const std::string& action_prefix,
+    std::string* action_value);
+
 // Searches for the specified Chrome-Proxy action, and if present interprets
 // its value as a duration in seconds.
 bool GetDataReductionProxyBypassDuration(