Add UMAs for checking header values against RFC 7230 in //net

net/http/http_response_headers.cc

Index: net/http/http_response_headers.cc
diff --git a/net/http/http_response_headers.cc b/net/http/http_response_headers.cc
index c535e0ab64e1d815972aede695d53b071770fa96..55dfb6bd71229e53d724fa05f5f189bf89f9e6ae 100644
--- a/net/http/http_response_headers.cc
+++ b/net/http/http_response_headers.cc
@@ -770,6 +770,10 @@ void HttpResponseHeaders::AddHeader(std::string::const_iterator name_begin,
                                     std::string::const_iterator name_end,
                                     std::string::const_iterator values_begin,
                                     std::string::const_iterator values_end) {
+  UMA_HISTOGRAM_BOOLEAN("Net.HttpResponseHeaderValueValidInRFC7230",
+                        HttpUtil::IsValidHeaderValueRFC7230(
+                            base::StringPiece(values_begin, values_end)));
+
   // If the header can be coalesced, then we should split it up.
   if (values_begin == values_end ||
       HttpUtil::IsNonCoalescingHeader(name_begin, name_end)) {