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..d4b6e2fe17ac0df2c13de59d17a84f9e84772fee 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(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)) {