[net/dns] Serve requests from HOSTS file if possible.

net/base/host_resolver.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_BASE_HOST_RESOLVER_H_
 #define NET_BASE_HOST_RESOLVER_H_
 #pragma once
 
 #include <string>
 
@@ skipping 114 matching lines @@
   // the async request. This handle is not valid after the request has
   // completed.
   //
   // Profiling information for the request is saved to |net_log| if non-NULL.
   virtual int Resolve(const RequestInfo& info,
                       AddressList* addresses,
                       const CompletionCallback& callback,
                       RequestHandle* out_req,
                       const BoundNetLog& net_log) = 0;
 
-  // Resolves the given hostname (or IP address literal) out of cache
-  // only.  This is guaranteed to complete synchronously.  This acts like
-  // |Resolve()| if the hostname is IP literal or cached value exists.
-  // Otherwise, ERR_DNS_CACHE_MISS is returned.
+  // Resolves the given hostname (or IP address literal) out of cache or HOSTS
+  // file (if enabled) only. This is guaranteed to complete synchronously.
+  // This acts like |Resolve()| if the hostname is IP literal, or cached value
+  // or HOSTS entry exists. Otherwise, ERR_DNS_CACHE_MISS is returned.
   virtual int ResolveFromCache(const RequestInfo& info,
                                AddressList* addresses,
                                const BoundNetLog& net_log) = 0;
 
   // Cancels the specified request. |req| is the handle returned by Resolve().
   // After a request is canceled, its completion callback will not be called.
   // CancelRequest must NOT be called after the request's completion callback
   // has already run or the request was canceled.
   virtual void CancelRequest(RequestHandle req) = 0;
 
@@ skipping 42 matching lines @@
 // As above, but the HostResolver will use the asynchronous DNS client in
 // DnsTransaction, which will be configured using DnsConfigService to match
 // the system DNS settings. If the client fails, the resolver falls back to
 // the global HostResolverProc.
 NET_EXPORT HostResolver* CreateAsyncHostResolver(size_t max_concurrent_resolves,
                                                  size_t max_retry_attempts,
                                                  NetLog* net_log);
 }  // namespace net
 
 #endif  // NET_BASE_HOST_RESOLVER_H_