Add finch configuration for the OfflinePagesSvelte finch test.

testing/variations/fieldtrial_testing_config.json

 {
     "AndroidSpellChecker": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Enabled_NonLowEnd",
                     "enable_features": [
@@ skipping 1302 matching lines @@
     ],
     "OfflinePagesAsyncLoading": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Enabled",
                     "enable_features": [
-                        "OfflinePagesAsyncDownload"
+                        "OfflinePagesAsyncDownload",
+                        "OfflinePagesSvelte"
                     ]
                 }
             ]
         }
     ],
     "OutOfProcessPac": [
         {
             "platforms": [
                 "chromeos",
                 "linux",
@@ skipping 1350 matching lines @@
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "use-new-media-cache"
                     ]
                 }
             ]
         }
     ]
 }