TRON log important auto-fill events

Example log from
android.autofillservice.cts.LoginActivityTest#testAutoFill#testAutoFillOneDatasetAndSave
(translated from numbers of human readable string):

AUTOFILL_SESSION_STARTED
   package=android.autofillservice.cts
AUTOFILL_REQUEST
   type=TYPE_SUCCESS
   package=android.autofillservice.cts
   FIELD_AUTOFILL_SERVICE=android.autofillservice.cts
   FIELD_AUTOFILL_NUM_DATASETS=1
AUTOFILL_FILL_UI
   type=TYPE_ACTION
   package=android.autofillservice.cts
   FIELD_AUTOFILL_NUM_DATASETS=1
   FIELD_AUTOFILL_FILTERTEXT_LEN=0
AUTOFILL_DATASET_APPLIED
   package=android.autofillservice.cts
   FIELD_AUTOFILL_NUM_VALUES=2
   FIELD_AUTOFILL_NUM_VIEWS_FILLED=2
AUTOFILL_SAVE_UI
   package=android.autofillservice.cts
   FIELD_AUTOFILL_NUM_IDS=2
AUTOFILL_DATA_SAVE_REQUEST
   type=TYPE_SUCCESS
   package=android.autofillservice.cts
   FIELD_AUTOFILL_SERVICE=android.autofillservice.cts
AUTOFILL_SESSION_FINISHED
   package=android.autofillservice.cts

Test: Ran auto-fill tests and looked at event log.
Change-Id: I58aaa58e4435e7d04c8cd91878411943d3eb13de