HostResolver supports optional CNAME lookups.

net/base/host_resolver_proc.cc

Index: net/base/host_resolver_proc.cc
diff --git a/net/base/host_resolver_proc.cc b/net/base/host_resolver_proc.cc
index 5ccf01afb4711a7e64919e23997a7fec04d2bb7c..feff5cfe837872bc6087aa6edc26a6a2c55335cc 100644
--- a/net/base/host_resolver_proc.cc
+++ b/net/base/host_resolver_proc.cc
@@ -67,14 +67,18 @@ HostResolverProc* HostResolverProc::GetDefault() {
   return default_proc_;
 }
 
-int HostResolverProc::ResolveUsingPrevious(const std::string& host,
-                                           AddressFamily address_family,
-                                           AddressList* addrlist) {
+int HostResolverProc::ResolveUsingPrevious(
+    const std::string& host,
+    AddressFamily address_family,
+    HostResolverFlags host_resolver_flags,
+    AddressList* addrlist) {
   if (previous_proc_)
-    return previous_proc_->Resolve(host, address_family, addrlist);
+    return previous_proc_->Resolve(host, address_family,
+                                   host_resolver_flags, addrlist);
 
   // Final fallback is the system resolver.
-  return SystemHostResolverProc(host, address_family, addrlist);
+  return SystemHostResolverProc(host, address_family,
+                                host_resolver_flags, addrlist);
 }
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
@@ -152,6 +156,7 @@ ThreadLocalStorage::Slot DnsReloadTimer::tls_index_(base::LINKER_INITIALIZED);
 
 int SystemHostResolverProc(const std::string& host,
                            AddressFamily address_family,
+                           HostResolverFlags host_resolver_flags,
                            AddressList* addrlist) {
   // The result of |getaddrinfo| for empty hosts is inconsistent across systems.
   // On Windows it gives the default interface's address, whereas on Linux it
@@ -205,6 +210,9 @@ int SystemHostResolverProc(const std::string& host,
   hints.ai_flags = AI_ADDRCONFIG;
 #endif
 
+  if (host_resolver_flags & HOST_RESOLVER_FLAGS_CANONNAME)
+    hints.ai_flags |= AI_CANONNAME;
+
   // Restrict result set to only this socket type to avoid duplicates.
   hints.ai_socktype = SOCK_STREAM;