Add finch configuration for the OfflinePagesSvelte finch test.

testing/variations/fieldtrial_testing_config.json

 {
     "AndroidSpellChecker": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Enabled_NonLowEnd",
                     "enable_features": [
@@ skipping 1304 matching lines @@
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "OfflinePagesAsyncDownload"
                     ]
+                },
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "OfflinePagesSvelte"

[jianli, 2017/01/26 01:32:34]

Should this be merged into above entries?

[Steven Holte, 2017/01/26 21:59:39]

Yes, assuming these will be controlled by the same finch config.  Just move
"OfflinePagesSvelte" into the enabled_features list.

[Pete Williamson, 2017/01/28 01:29:13]

Done.

+                    ]
                 }
             ]
         }
     ],
     "OutOfProcessPac": [
         {
             "platforms": [
                 "chromeos",
                 "linux",
                 "mac",
@@ skipping 1334 matching lines @@
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "use-new-media-cache"
                     ]
                 }
             ]
         }
     ]
 }