Add APK targets to build libjingle tests for Android.

webrtc/system_wrappers/source/field_trial_default.cc

Index: webrtc/system_wrappers/source/field_trial_default.cc
diff --git a/webrtc/system_wrappers/source/field_trial_default.cc b/webrtc/system_wrappers/source/field_trial_default.cc
index 1a9bd6bc79f8036c82828a272da79b01ad2d5524..0e2c286117a1a2cc96687c61b5f6c2483b0e4c37 100644
--- a/webrtc/system_wrappers/source/field_trial_default.cc
+++ b/webrtc/system_wrappers/source/field_trial_default.cc
@@ -58,5 +58,9 @@ void InitFieldTrialsFromString(const char* trials_string) {
   trials_init_string = trials_string;
 }
 
+const char* GetFieldTrialString() {
+  return trials_init_string;
+}
+
 }  // namespace field_trial
 }  // namespace webrtc