Minor improvements to MockLogDnsTraffic

components/certificate_transparency/mock_log_dns_traffic.h

Index: components/certificate_transparency/mock_log_dns_traffic.h
diff --git a/components/certificate_transparency/mock_log_dns_traffic.h b/components/certificate_transparency/mock_log_dns_traffic.h
index f91e66824de64b4a0b1d63914ca54da1977eb80a..bf9391789968a62eefdb6f0f068c40b1270a96c9 100644
--- a/components/certificate_transparency/mock_log_dns_traffic.h
+++ b/components/certificate_transparency/mock_log_dns_traffic.h
@@ -73,10 +73,25 @@ class MockSocketData {
 
 // Mocks DNS requests and responses for a Certificate Transparency (CT) log.
 // This is implemented using mock sockets. Call the CreateDnsClient() method to
 // get a net::DnsClient wired up to these mock sockets.
 // The Expect*() methods must be called from within a GTest test case.
+//
+// Example Usage:
+// // Create a mock NetworkChangeNotifier to propogate DNS config.
+// std::unique_ptr<net::NetworkChangeNotifier> net_change_notifier =
+//     net::NetworkChangeNotifier::CreateMock();
+//
+// MockLogDnsTraffic mock_dns;
+// mock_dns.InitializeDnsConfig();
+// // Use the Expect* methods to define expected DNS requests and responses.
+// mock_dns.ExpectLeafIndexRequestAndResponse(
+//     "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
+//     "123456");
+//
+// LogDnsClient log_client(mock_dns.CreateDnsClient(), ...);
+// log_client.QueryLeafIndex("ct.test", ...);

[Eran Messeri, 2016/09/20 14:31:04]

Which message loop should be pumped to guarantee the callback has been invoked?

[Rob Percival, 2016/09/20 16:33:11]

I've added a few more lines to the example usage to show that a
MessageLoopWithIO should be used.

 class MockLogDnsTraffic {
  public:
   MockLogDnsTraffic();
   ~MockLogDnsTraffic();
 
@@ -124,10 +139,12 @@ class MockLogDnsTraffic {
   // Creates a DNS client that uses mock sockets.
   // It is this DNS client that the expectations will be tested against.
   std::unique_ptr<net::DnsClient> CreateDnsClient();
 
   // Sets whether mock reads should complete synchronously or asynchronously.
+  // By default, they complete asynchronously. The only reason to change this
+  // is to test that LogDnsClient handles both modes in the same way.
   void SetSocketReadMode(net::IoMode read_mode) {
     socket_read_mode_ = read_mode;
   }
 
  private: