DNS: Support reprioritization of requests.

net/dns/host_resolver.cc

Index: net/dns/host_resolver.cc
diff --git a/net/dns/host_resolver.cc b/net/dns/host_resolver.cc
index abe8e49e6578714bf5216398b3450135b4798da1..f0a751e767df0f71dcd42acc1051effa72616b58 100644
--- a/net/dns/host_resolver.cc
+++ b/net/dns/host_resolver.cc
@@ -103,6 +103,11 @@ HostResolver::~HostResolver() {
 void HostResolver::SetDnsClientEnabled(bool enabled) {
 }
 
+void HostResolver::ChangeRequestPriority(RequestHandle req,
+                                         RequestPriority priority) {
+  NOTIMPLEMENTED();
+}
+
 HostCache* HostResolver::GetHostCache() {
   return NULL;
 }