Add APK targets to build libjingle tests for Android.

webrtc/system_wrappers/include/field_trial_default.h

 //
 // Copyright (c) 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_SYSTEM_WRAPPERS_INCLUDE_FIELD_TRIAL_DEFAULT_H_
 #define WEBRTC_SYSTEM_WRAPPERS_INCLUDE_FIELD_TRIAL_DEFAULT_H_
 
 namespace webrtc {
 namespace field_trial {
 
 // Optionally initialize field trial from a string.
 // This method can be called at most once before any other call into webrtc.
 // E.g. before the peer connection factory is constructed.
 // Note: trials_string must never be destroyed.
 void InitFieldTrialsFromString(const char* trials_string);
 
+const char* GetFieldTrialString();
+
 }  // namespace field_trial
 }  // namespace webrtc
 
 #endif  // WEBRTC_SYSTEM_WRAPPERS_INCLUDE_FIELD_TRIAL_DEFAULT_H_