Enable cpplint and fix cpplint errors in webrtc/api

webrtc/api/fakemetricsobserver.h

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_API_FAKEMETRICSOBSERVER_H_
 #define WEBRTC_API_FAKEMETRICSOBSERVER_H_
 
 #include <map>
 #include <string>
+#include <vector>
 
 #include "webrtc/api/peerconnectioninterface.h"
 #include "webrtc/base/thread_checker.h"
 
 namespace webrtc {
 
 class FakeMetricsObserver : public MetricsObserverInterface {
  public:
   FakeMetricsObserver();
   void Reset();
@@ skipping 16 matching lines @@
   // The vector contains maps for each counter type. In the map, it's a mapping
   // from individual counter to its count, such that it's memory efficient when
   // comes to sparse enum types, like the SSL ciphers in the IANA registry.
   std::vector<std::map<int, int>> counters_;
   int histogram_samples_[kPeerConnectionMetricsName_Max];
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_FAKEMETRICSOBSERVER_H_