Add support for get_experiment_tokens_api please

Add support for get_experiment_tokens_api please.

Related to #897

16:56:03.553 E/GH.PhenotypeCommitter(22102): Failed to update Car Policy experiment tokens!
16:56:03.553 E/GH.PhenotypeCommitter(22102): may: Missing Feature{name=get_experiment_tokens_api, version=1}
16:56:03.553 E/GH.PhenotypeCommitter(22102): 	at mbz.q(SourceFile:10)
16:56:03.553 E/GH.PhenotypeCommitter(22102): 	at mbz.h(SourceFile:3)
16:56:03.553 E/GH.PhenotypeCommitter(22102): 	at mcd.handleMessage(SourceFile:104)
16:56:03.553 E/GH.PhenotypeCommitter(22102): 	at android.os.Handler.dispatchMessage(Handler.java:102)
16:56:03.820 I/wm_task_removed(730): [59,removeAppToken: last token]
16:56:03.553 E/GH.PhenotypeCommitter(22102): 	at android.os.Looper.loop(Looper.java:164)
16:56:03.821 I/wm_task_removed(730): [59,removeTask]
16:56:03.553 E/GH.PhenotypeCommitter(22102): 	at android.os.HandlerThread.run(HandlerThread.java:65)
16:56:03.825 I/am_on_stop_called(22582): [0,com.google.android.gearhead.vanagon.overview.VnConfirmExitActivity,destroy]
16:56:03.554 E/GH.PhenotypeCommitter(22102): Failed to update Gearhead experiment tokens!
16:56:03.554 E/GH.PhenotypeCommitter(22102): may: Missing Feature{name=get_experiment_tokens_api, version=1}
16:56:03.841 I/wm_task_removed(730): [62,removeAppToken: last token]
16:56:03.554 E/GH.PhenotypeCommitter(22102): 	at mbz.q(SourceFile:10)
16:56:03.843 I/wm_task_removed(730): [62,removeTask]
16:56:03.554 E/GH.PhenotypeCommitter(22102): 	at mbz.h(SourceFile:3)
16:56:03.554 E/GH.PhenotypeCommitter(22102): 	at mcd.handleMessage(SourceFile:104)
16:56:03.554 E/GH.PhenotypeCommitter(22102): 	at android.os.Handler.dispatchMessage(Handler.java:102)
16:56:03.554 E/GH.PhenotypeCommitter(22102): 	at android.os.Looper.loop(Looper.java:164)
16:56:03.554 E/GH.PhenotypeCommitter(22102): 	at android.os.HandlerThread.run(HandlerThread.java:65)
...
16:56:03.701 W/GH.CarClientManager(22582): getToken() called while client was disconnected!
16:56:03.701 W/GH.CarClientManager(22582): java.lang.RuntimeException: Current stack
16:56:03.701 W/GH.CarClientManager(22582): 	at djc.s(SourceFile:3)
16:56:03.701 W/GH.CarClientManager(22582): 	at djc.e(SourceFile:1)
16:56:03.701 W/GH.CarClientManager(22582): 	at ehy.f(SourceFile:2)
16:56:03.701 W/GH.CarClientManager(22582): 	at jeg.i(SourceFile:5)
16:56:03.701 W/GH.CarClientManager(22582): 	at jeg.b(SourceFile:13)
16:56:03.701 W/GH.CarClientManager(22582): 	at jdw.c(SourceFile:12)
16:56:03.701 W/GH.CarClientManager(22582): 	at com.google.android.gearhead.vanagon.thirdparty.CarModeSysUI.h(SourceFile:4)
16:56:03.701 W/GH.CarClientManager(22582): 	at com.google.android.gearhead.vanagon.thirdparty.CarModeSysUI.onStop(SourceFile:5)
16:56:03.701 W/GH.CarClientManager(22582): 	at java.lang.reflect.Method.invoke(Native Method)
16:56:03.701 W/GH.CarClientManager(22582): 	at com.google.android.apps.auto.sdk.vanagon.PhoneSysUiClient.c(SourceFile:3)
16:56:03.701 W/GH.CarClientManager(22582): 	at jat.onStop(SourceFile:10)
16:56:03.701 W/GH.CarClientManager(22582): 	at jak.onStop(SourceFile:2)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.app.Instrumentation.callActivityOnStop(Instrumentation.java:1375)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.app.Activity.performStop(Activity.java:7181)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:4032)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.app.ActivityThread.handleStopActivity(ActivityThread.java:4084)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.app.ActivityThread.-wrap24(Unknown Source:0)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1622)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.os.Handler.dispatchMessage(Handler.java:106)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.os.Looper.loop(Looper.java:164)
16:56:03.701 W/GH.CarClientManager(22582): 	at android.app.ActivityThread.main(ActivityThread.java:6494)
16:56:03.701 W/GH.CarClientManager(22582): 	at java.lang.reflect.Method.invoke(Native Method)
16:56:03.701 W/GH.CarClientManager(22582): 	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:440)
16:56:03.701 W/GH.CarClientManager(22582): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
16:56:03.701 W/GH.CarClientManager(22582): 	at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:108)

No source file or test is named. Start by investigating the PhenotypeCommitter messages for get_experiment_tokens_api and the related issue #897, then trace the CarClientManager token path shown in the log. Done should include support for the requested API and no corresponding missing-feature or disconnected-client failures.