net: add IsMethodIdempotent() to HttpUtil

net/http/http_util.h

Index: net/http/http_util.h
diff --git a/net/http/http_util.h b/net/http/http_util.h
index 5903238288a4ca1149414e3c11356fb59f9224f2..8f84ce1434a54efbcf0f753b0acab9e4ab92e06f 100644
--- a/net/http/http_util.h
+++ b/net/http/http_util.h
@@ -75,9 +75,14 @@ class NET_EXPORT HttpUtil {
                                     base::Time now,
                                     base::TimeDelta* retry_after);
 
-  // True if the request method is "safe" (per section 4.2.1 of RFC 7231).
+  // Returns true if the request method is "safe" (per section 4.2.1 of
+  // RFC 7231).
   static bool IsMethodSafe(const std::string& method);
 
+  // Returns true if the request method is idempotent (per section 4.2.2 of
+  // RFC 7231).
+  static bool IsMethodIdempotent(const std::string& method);
+
   // Returns true if it is safe to allow users and scripts to specify the header
   // named |name|.
   static bool IsSafeHeader(const std::string& name);