[Zine] Adding group for 10% enabled for new favicon server in fieldtrial_testing_config.json

Bug: 714109
Change-Id: Icc18f9cf5d338e3c9ae213a2bd8697d4c11674a1
Reviewed-on: https://chromium-review.googlesource.com/1207711Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Filip Gorski <fgorski@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589012}

testing/variations/fieldtrial_testing_config.json

@@ -2454,6 +2454,12 @@
                     "enable_features": [
                         "ContentSuggestionsFaviconsFromNewServer"
                     ]
+                },
+                {
+                    "name": "Enabled_10",
+                    "enable_features": [
+                        "ContentSuggestionsFaviconsFromNewServer"
+                    ]
                 }
             ]
         }