Fix failing sync integration tests.
TwoClientLivePreferencesSyncTest.Security was failing due to a couple of
EXPECT_NEs that ought to have been EXPECT_EQs.
TwoClientLiveAutofillSyncTest.Client1HasData was failing due to a change
in autofill behavior introduced in r55781 to fix security bug crbug.com/51727.
This changelist also includes a clarification in the logic used by