Add a flag needed for Autofill tests to test_runner.py.

This was configured in my scheme when testing locally, so I forgot it
even existed. Found when doing a full repro of the bot testing flow
while trying to debug unrelated issues with ios-wpr-simulator.

This line is very long as both of these flags should be part of "-c"
so that iossim passes it properly. Is that fine?

Bug: 892381
Change-Id: I5d7def3f138d10033914718429307b76a8d71d8a
Reviewed-on: https://chromium-review.googlesource.com/c/1311809
Commit-Queue: ericale <ericale@chromium.org>
Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604615}

ios/build/bots/scripts/test_runner.py

@@ -1103,7 +1103,8 @@ class WprProxySimulatorTestRunner(SimulatorTestRunner):
           recipe_cmd = [
             self.iossim_path, '-d', self.platform, '-s',
             self.version, '-t', 'AutofillAutomationTestCase', '-c',
-            '-autofillautomation={}'.format(recipePath),
+            '--enable-features=AutofillShowTypePredictions {}={}'.format(
+              '-autofillautomation', recipePath),
             '-u', udid,
           ]
           for env_var in self.env_vars: