Enabled AutofillServerBehaviors on android_webview as well

TBR=isherman@chromium.org

Bug: 956560
Change-Id: Ie5cf8a193452c0281b8770eaab4f3d0eb107bb34
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1986076Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728242}

testing/variations/fieldtrial_testing_config.json

@@ -1023,6 +1023,7 @@
         {
             "platforms": [
                 "android",
+                "android_webview",
                 "chromeos",
                 "ios",
                 "linux",