add Chromium field trial config files

testing/variations/fieldtrial_testing_config_win.json

 {
     "BrowserBlacklist": [
         {
             "group_name": "Enabled"
         }
     ],
     "CTRequiredForEVTrial": [
         {
             "group_name": "RequirementEnforced"
         }
@@ skipping 71 matching lines @@
     "SettingsEnforcement": [
         {
             "group_name": "enforce_always_with_extensions_and_dse"
         }
     ],
     "ShowAppLauncherPromo": [
         {
             "group_name": "ShowPromoUntilDismissed"
         }
     ],
+    "SyncBackingDatabase32K": [
+        {
+            "group_name": "Enabled"
+        },
+        {
+            "group_name": "Disabled"
+        }
+    ],
     "UwSInterstitialStatus": [
         {
             "group_name": "On"
         }
     ],
     "VoiceTrigger": [
         {
             "group_name": "Install"
         }
     ]
 }