Adding Short Record Header feature.

testing/variations/fieldtrial_testing_config.json

 {
     "AndroidSessionNotifications": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Disabled"
                 }
@@ skipping 2194 matching lines @@
                 "linux",
                 "mac",
                 "win"
             ],
             "experiments": [
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "NegotiateTLS13"
                     ]
+                },
+                {
+                    "name": "EnabledWithShortRecordHeader",
+                    "enable_features": [
+                        "NegotiateTLS13",
+                        "SSLShortRecordHeader"
+                    ]
                 }
             ]
         }
     ],
     "TabManagementExperiment": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
@@ skipping 302 matching lines @@
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "use-new-media-cache"
                     ]
                 }
             ]
         }
     ]
 }