net: add IsMethodIdempotent() to HttpUtil

net/http/http_util.cc

Index: net/http/http_util.cc
diff --git a/net/http/http_util.cc b/net/http/http_util.cc
index 5f7c8531e8828d9914a1d2e7bf8e5288eb20b6c9..95ba606a7e0fa239a9c8c62f19591ec6bb39097a 100644
--- a/net/http/http_util.cc
+++ b/net/http/http_util.cc
@@ -351,6 +351,11 @@ bool HttpUtil::IsMethodSafe(const std::string& method) {
 }
 
 // static
+bool HttpUtil::IsMethodIdempotent(const std::string& method) {
+  return IsMethodSafe(method) || method == "PUT" || method == "DELETE";
+}
+
+// static
 bool HttpUtil::IsSafeHeader(const std::string& name) {
   std::string lower_name(base::ToLowerASCII(name));
   if (base::StartsWith(lower_name, "proxy-", base::CompareCase::SENSITIVE) ||