HostResolver supports optional CNAME lookups.

net/base/host_resolver_proc.h

Index: net/base/host_resolver_proc.h
diff --git a/net/base/host_resolver_proc.h b/net/base/host_resolver_proc.h
index ca0c55d3f5bf45afdaf28934e8eef5f4851393f1..6f32280489dac5f11777667064131e608afa33c5 100644
--- a/net/base/host_resolver_proc.h
+++ b/net/base/host_resolver_proc.h
@@ -30,6 +30,7 @@ class HostResolverProc : public base::RefCountedThreadSafe<HostResolverProc> {
   // a list of socket addresses. Otherwise returns a network error code.
   virtual int Resolve(const std::string& host,
                       AddressFamily address_family,
+                      HostResolverFlags host_resolver_flags,
                       AddressList* addrlist) = 0;
 
  protected:
@@ -40,6 +41,7 @@ class HostResolverProc : public base::RefCountedThreadSafe<HostResolverProc> {
   // Asks the fallback procedure (if set) to do the resolve.
   int ResolveUsingPrevious(const std::string& host,
                            AddressFamily address_family,
+                           HostResolverFlags host_resolver_flags,
                            AddressList* addrlist);
 
  private:
@@ -78,6 +80,7 @@ class HostResolverProc : public base::RefCountedThreadSafe<HostResolverProc> {
 // network error code.
 int SystemHostResolverProc(const std::string& host,
                            AddressFamily address_family,
+                           HostResolverFlags host_resolver_flags,
                            AddressList* addrlist);
 
 }  // namespace net