Skip IPv6 probes when resolving IPv4 literals. The probes aren't

net/dns/host_resolver_impl.cc

Index: net/dns/host_resolver_impl.cc
diff --git a/net/dns/host_resolver_impl.cc b/net/dns/host_resolver_impl.cc
index 98e410551e9c3599de5d64b2a7a8ca6fc01267d1..2081864319531d96bbd0a569eede6f9ca34a29e1 100644
--- a/net/dns/host_resolver_impl.cc
+++ b/net/dns/host_resolver_impl.cc
@@ -49,6 +49,7 @@
 #include "net/dns/host_resolver_proc.h"
 #include "net/socket/client_socket_factory.h"
 #include "net/udp/datagram_client_socket.h"
+#include "url/url_canon_ip.h"
 
 #if defined(OS_WIN)
 #include "net/base/winsock_init.h"
@@ -2154,7 +2155,14 @@ HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
   AddressFamily effective_address_family = info.address_family();
 
   if (info.address_family() == ADDRESS_FAMILY_UNSPECIFIED) {
-    if (probe_ipv6_support_ && !use_local_ipv6_) {
+    IPAddressNumber ip_number;
+    url::Component host_comp(0, info.hostname().size());
+    int num_components;
+    if (probe_ipv6_support_ && !use_local_ipv6_ &&
+        // Don't bother IPv6 probing when resolving IPv4 literals.
+        url::IPv4AddressToNumber(info.hostname().data(), host_comp,
+                                 &ip_number[0],
+                                 &num_components) != url::CanonHostInfo::IPV4) {

[mmenke, 2015/02/13 15:03:27]

Doing this twice seems weird...Maybe we should just do the ResolveAsIP call
first?  I suppose if we care about not resolving IPv6 literals when we have no
IPv6 support, we still have to do the probe, but I'm skeptical whether we really
get anything from that.

[pauljensen, 2015/02/13 15:33:08]

I changed the code to parse it just once.  WDYT?

       // Google DNS address.
       const uint8 kIPv6Address[] =
           { 0x20, 0x01, 0x48, 0x60, 0x48, 0x60, 0x00, 0x00,