Moved transport.h from webrtc/ to webrtc/api, created build target and updated dependencies.

webrtc/api/api.gyp

Index: webrtc/api/api.gyp
diff --git a/webrtc/api/api.gyp b/webrtc/api/api.gyp
index d017cda2d621f18b51e05a48ba8027ca580e9a7c..6bbe2dd04643f1b603ddb3d331e1d55ebf48aaaf 100644
--- a/webrtc/api/api.gyp
+++ b/webrtc/api/api.gyp
@@ -99,6 +99,7 @@
       'type': 'static_library',
       'dependencies': [
         # TODO(kjellander): Add remaining dependencies when webrtc:4243 is done.
+        ':transport_api',
         '<(webrtc_root)/base/base.gyp:rtc_base_approved',
         '<(webrtc_root)/common.gyp:webrtc_common',
         '<(webrtc_root)/modules/modules.gyp:audio_encoder_interface',
@@ -231,5 +232,13 @@
         'stats/rtcstatsreport.h',
       ],
     },  # target rtc_stats_api
+    {
+      # GN version: webrtc/api:transport_api
+      'target_name': 'transport_api',
+      'type': 'static_library',
+      'sources': [
+        'call/transport.h',
+      ],
+    }
   ],  # targets
 }