[Sync] Enable USS implementation of Autocomplete by default

USS Autocomplete is being launched on stable. It needs to be enabled by
default on ToT.

BUG=702711
R=pnoland@chromium.org

Change-Id: I10b32e8d948728ef8f4d98841639e6e862378a4d
Reviewed-on: https://chromium-review.googlesource.com/779633Reviewed-by: Patrick Noland <pnoland@google.com>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Pavel Yatsuk <pavely@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518268}

components/sync/driver/sync_driver_switches.cc

@@ -51,7 +51,7 @@ const base::Feature kSyncUserTranslationEvents{
 
 // Enables USS implementation of Autocomplete datatype.
 const base::Feature kSyncUSSAutocomplete{"SyncUSSAutocomplete",
-                                         base::FEATURE_DISABLED_BY_DEFAULT};
+                                         base::FEATURE_ENABLED_BY_DEFAULT};
 
 // Enable USS implementation of Bookmarks datatype.
 const base::Feature kSyncUSSBookmarks{"SyncUSSBookmarks",

testing/variations/fieldtrial_testing_config.json

@@ -3544,26 +3544,6 @@
             ]
         }
     ],
-    "SyncUSSAutocomplete": [
-        {
-            "platforms": [
-                "android",
-                "chromeos",
-                "ios",
-                "linux",
-                "mac",
-                "win"
-            ],
-            "experiments": [
-                {
-                    "name": "Enabled",
-                    "enable_features": [
-                        "SyncUSSAutocomplete"
-                    ]
-                }
-            ]
-        }
-    ],
     "TLS13Variant": [
         {
             "platforms": [