[ChromeDriver] Add support for attaching multiple DevToolsEventListeners to a DevToolsClient.

chrome/test/chromedriver/chrome_impl_unittest.cc

 // 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.
 
 #include <list>
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
@@ skipping 77 matching lines @@
   }
   virtual Status SendCommandAndGetResult(
       const std::string& method,
       const base::DictionaryValue& params,
       scoped_ptr<base::DictionaryValue>* result) OVERRIDE {
     if (status_.IsError())
       return status_;
     result->reset(result_.DeepCopy());
     return Status(kOk);
   }
+  virtual void AddListener(DevToolsEventListener* listener) OVERRIDE {}
 
  private:
   Status status_;
   base::DictionaryValue result_;
 };
 
 void AssertEvalFails(const base::DictionaryValue& command_result) {
   scoped_ptr<base::DictionaryValue> result;
   FakeDevToolsClient client;
   client.set_result(command_result);
@@ skipping 118 matching lines @@
   FakeDevToolsClient client;
   base::DictionaryValue dict;
   dict.SetBoolean("wasThrown", false);
   dict.SetString("result.objectId", "id");
   client.set_result(dict);
   std::string object_id;
   ASSERT_TRUE(internal::EvaluateScriptAndGetObject(
       &client, 0, "", &object_id).IsOk());
   ASSERT_STREQ("id", object_id.c_str());
 }