SimpleCache: Add fieldtrial testing information.

testing/variations/fieldtrial_testing_config_mac.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
@@ skipping 185 matching lines @@
     "SchedulerExpensiveTaskBlocking": [
         {
             "group_name": "Enabled"
         }
     ],
     "SdchPersistence": [
         {
             "group_name": "Enabled"
         }
     ],
+    "SimpleCacheTrial": [
+        {
+            "group_name": "ExperimentYes"
+        }
+    ],
     "SpdyEnableDependencies": [
         {
             "group_name": "Enable"
         }
     ],
     "StrictSecureCookies": [
         {
             "group_name": "Enabled"
         }
     ],
@@ skipping 51 matching lines @@
     ],
     "use-new-media-cache": [
         {
             "enable_features": [
                 "use-new-media-cache"
             ],
             "group_name": "Enabled"
         }
     ]
 }