Probing: Add support for exponential startup probing

webrtc/modules/congestion_controller/congestion_controller.gypi

 # Copyright (c) 2016 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.
 
 {
   'targets': [
     {
       'target_name': 'congestion_controller',
       'type': 'static_library',
       'dependencies': [
         '<(webrtc_root)/modules/modules.gyp:bitrate_controller',
         '<(webrtc_root)/modules/modules.gyp:paced_sender',
         '<(webrtc_root)/modules/modules.gyp:remote_bitrate_estimator',
       ],
       'sources': [
         'congestion_controller.cc',
         'delay_based_bwe.cc',
         'delay_based_bwe.h',
         'include/congestion_controller.h',
         'probe_bitrate_estimator.cc',
         'probe_bitrate_estimator.h',
+        'probe_controller.cc',
+        'probe_controller.h',
       ],
       # TODO(jschuh): Bug 1348: fix size_t to int truncations.
       'msvs_disabled_warnings': [ 4267, ],
     },
   ], # targets
 }