Track how often we successfully resolve non-'compliant' domain names.

net/dns/host_resolver_proc.cc

Index: net/dns/host_resolver_proc.cc
diff --git a/net/dns/host_resolver_proc.cc b/net/dns/host_resolver_proc.cc
index 4bed222a21562339d026ea440c2968ce27caca5a..f1253ad9ce9dfdd5ad3ddd142c1829d7fe3b8b49 100644
--- a/net/dns/host_resolver_proc.cc
+++ b/net/dns/host_resolver_proc.cc
@@ -7,6 +7,7 @@
 #include "build/build_config.h"
 
 #include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/sys_byteorder.h"
 #include "net/base/address_list.h"
 #include "net/base/net_errors.h"
@@ -125,10 +126,14 @@ int SystemHostResolverCall(const std::string& host,
                            HostResolverFlags host_resolver_flags,
                            AddressList* addrlist,
                            int* os_error) {
-  // Make sure |host| is properly formed.
+  // Make sure |host| is properly formed. Save the validity check result so that
+  // we can count how often invalid names (see |net::IsValidHostLabelCharacter|)
+  // successfully resolve, if ever. TODO(crbug.com/695474): Remove this when we
+  // no longer need the UMA metrics.

[Ryan Sleevi, 2017/06/02 13:39:55]

https://groups.google.com/a/chromium.org/forum/#!topic/chromium-dev/NH-S6KCkr2M

// Make sure |host| is properly formed. Record whether or not the name was valid
(see
// net::IsValidHostLabelCharacter), so that it's possible to measure how often
invalid
// names successfully resolve.
// TODO(https://crbug.com/695474): Remove this once invalid names are
consistently
// rejected.

+  bool valid_hostname = false;
   {
     std::string out_ignored;
-    if (!DNSDomainFromDot(host, &out_ignored))
+    if (!DNSDomainFromDotWithValidityCheck(host, &out_ignored, &valid_hostname))
       return ERR_NAME_NOT_RESOLVED;
   }
 
@@ -253,6 +258,8 @@ int SystemHostResolverCall(const std::string& host,
 
   *addrlist = AddressList::CreateFromAddrinfo(ai);
   freeaddrinfo(ai);
+  UMA_HISTOGRAM_BOOLEAN("Net.SuccessfulResolutionWithValidDNSName",
+                        valid_hostname);
   return OK;
 }