[AF] Added fieldtrial testing config for AutofillOffNoServerData.

I also had to remove the autocomplete="off" from a lot of
FormStructureBrowserTest test cases. Basically, since we're not really
querying the Autofill server during browser tests, then all of the
"server" predictions are set as NO_SERVER_DATA. Now, in conjunction
with the AutofillOffNoServerData, this means that any input in these
tests that has autocomplete="off" would have their predicted type
overwritten as UNKNOWN_TYPE. To make sure that the tests still cover
client-side heuristics (like they were intending to), I'm removing the
autocomplete="off" attributes from failing tests, which means they're
now properly testing these heuristics.

Bug: 949784
Change-Id: I2c0c3f20e5ccd01936510c2461e9ebd8c477fb45
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1569745
Commit-Queue: Sebastien Lalancette <seblalancette@chromium.org>
Reviewed-by: Fabio Tirelo <ftirelo@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#651842}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e36922ddfdf761b8a1cd5419b1bfe8284ea3fb90
1 file changed