Add histograms to measure DNS lookups for different configurations.

net/base/host_resolver_impl.cc

Index: net/base/host_resolver_impl.cc
===================================================================
--- net/base/host_resolver_impl.cc	(revision 87899)
+++ net/base/host_resolver_impl.cc	(working copy)
@@ -660,6 +660,20 @@
         category = RESOLVE_SPECULATIVE_SUCCESS;
         DNS_HISTOGRAM("DNS.ResolveSpeculativeSuccess", duration);
       }
+
+      // Log DNS lookups based on address_family.  This will help us determine
+      // if IPv4 or IPv4/6 lookups are faster or slower.
+      switch(key_.address_family) {
+        case ADDRESS_FAMILY_IPV4:
+          DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV4", duration);
+          break;
+        case ADDRESS_FAMILY_IPV6:
+          DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_IPV6", duration);
+          break;
+        case ADDRESS_FAMILY_UNSPECIFIED:
+          DNS_HISTOGRAM("DNS.ResolveSuccess_FAMILY_UNSPEC", duration);
+          break;

[jar (doing other things), 2011/06/09 18:30:00]

nit: perchance add a default: NOT_REACHED.

The style guide suggests this for non-enumerated cases, but also claims that in
enumerated cases the compiler will warn.... but I doubt our compiler provides
such a warning.

[cbentzel, 2011/06/09 18:47:03]

I've had compiler warnings for that case [I believe gcc on Linux does, perhaps
others]. 

+      }
     } else {
       if (had_non_speculative_request_) {
         category = RESOLVE_FAIL;
@@ -668,6 +682,19 @@
         category = RESOLVE_SPECULATIVE_FAIL;
         DNS_HISTOGRAM("DNS.ResolveSpeculativeFail", duration);
       }
+      // Log DNS lookups based on address_family.  This will help us determine
+      // if IPv4 or IPv4/6 lookups are faster or slower.
+      switch(key_.address_family) {
+        case ADDRESS_FAMILY_IPV4:
+          DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV4", duration);
+          break;
+        case ADDRESS_FAMILY_IPV6:
+          DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_IPV6", duration);
+          break;
+        case ADDRESS_FAMILY_UNSPECIFIED:
+          DNS_HISTOGRAM("DNS.ResolveFail_FAMILY_UNSPEC", duration);
+          break;
+      }
       UMA_HISTOGRAM_CUSTOM_ENUMERATION(kOSErrorsForGetAddrinfoHistogramName,
                                        std::abs(os_error),
                                        GetAllGetAddrinfoOSErrors());