[net/dns] Refactoring of DnsConfigService.

- Replaces Observer with Callback.
- The Callback is run within 100ms of any config change, not only on
  successful read. It is also run on errors in watches (registry and
  files). This allows HostResolverImpl to withdraw from using DnsTask
  until DnsConfig is read successfully.
- Moves DnsHostsReader to dns_hosts.{h,cc}).
- Handles missing HOSTS files.
- Respects network adapter binding order in DnsConfigServiceWin.
- Adds NetLog source for DnsConfig-related events.

BUG=112856, 115460, 115494
TEST=./net_unittests --gtest_filter=DnsConfig*

Review URL: http://codereview.chromium.org/9597029

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@127190 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 30 insertions, 1 deletions

diff --git a/net/dns/dns_hosts.h b/net/dns/dns_hosts.h
index fda7733..91c35ba 100644
--- a/net/dns/dns_hosts.h
+++ b/net/dns/dns_hosts.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -11,9 +11,12 @@
 #include <utility>
 #include <vector>
 
+#include "base/callback.h"
+#include "base/file_path.h"
 #include "net/base/address_family.h"
 #include "net/base/net_export.h"
 #include "net/base/net_util.h"  // can't forward-declare IPAddressNumber
+#include "net/dns/serial_worker.h"
 
 namespace net {
 
@@ -35,6 +38,32 @@ typedef std::map<DnsHostsKey, IPAddressNumber> DnsHosts;
 void NET_EXPORT_PRIVATE ParseHosts(const std::string& contents,
                                    DnsHosts* dns_hosts);
 
+// A SerialWorker that reads a HOSTS file and runs Callback.
+// Call WorkNow() to indicate file needs to be re-read.
+// Call Cancel() to disable the callback.
+class NET_EXPORT_PRIVATE DnsHostsReader
+    : NON_EXPORTED_BASE(public SerialWorker) {
+ public:
+  typedef base::Callback<void(const DnsHosts& hosts)> CallbackType;
+
+  DnsHostsReader(const FilePath& path, const CallbackType& callback);
+
+ private:
+  virtual ~DnsHostsReader();
+
+  virtual void DoWork() OVERRIDE;
+  virtual void OnWorkFinished() OVERRIDE;
+
+  FilePath path_;
+  CallbackType callback_;
+  // Written in DoWork, read in OnWorkFinished, no locking necessary.
+  DnsHosts dns_hosts_;
+  bool success_;
+
+  DISALLOW_COPY_AND_ASSIGN(DnsHostsReader);
+};
+
+
 }  // namespace net
 
 #endif  // NET_DNS_DNS_HOSTS_H_