[Android] Add an about flag for Download Manager UI

testing/variations/fieldtrial_testing_config_android.json

Index: testing/variations/fieldtrial_testing_config_android.json
diff --git a/testing/variations/fieldtrial_testing_config_android.json b/testing/variations/fieldtrial_testing_config_android.json
index c43005445e093dc66d0be7dc219047e7b20b61b5..e6ab328af340491423884a8e3e094c3c5023e261 100644
--- a/testing/variations/fieldtrial_testing_config_android.json
+++ b/testing/variations/fieldtrial_testing_config_android.json
@@ -129,6 +129,11 @@
             }
         }
     ],
+    "DownloadsUi": [
+        {
+            "group_name": "Disabled"
+        }
+    ],

[Ilya Sherman, 2016/08/10 05:59:51]

Hmm, could you please email/IM me with a link to the google3 config for this
field trial?  If you are not currently controlling this field trial server-side,
I don't think there's a need to add this kind of test coverage for the field
trial control.

FWIW, if you do need to add test coverage, you'll need to specify
disable_features.

     "EnableMediaThreadForMediaPlayback": [
         {
             "group_name": "Enabled"