Add Brotli to the experiment config

testing/variations/fieldtrial_testing_config.json

 {
     "AndroidSpellChecker": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Enabled_NonLowEnd",
                     "enable_features": [
@@ skipping 367 matching lines @@
             ]
         }
     ],
     "DataReductionProxyServerExperiments": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
-                    "name": "Prefetch",
+                    "name": "Brotli",
                     "params": {
-                        "exp": "prefetch"
+                        "exp": "allow_brotli"
                     }
                 },
                 {
                     "name": "Control1",
                     "params": {
                         "exp": "finch_control1"
                     }
                 },
                 {
                     "name": "Control2",
@@ skipping 2153 matching lines @@
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "use-new-media-cache"
                     ]
                 }
             ]
         }
     ]
 }