Add an environment variable toggle to control new service protocol auth token

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index 46660778468927c9ac5a04ddbac79c6a3f164468..bd1e6affac4230458b7aebe253dcf0a84543837f 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -832,6 +832,8 @@ static Dart_Isolate CreateIsolateAndSetupHelper(const char* script_uri,
       result = Dart_CompileAll();
       CHECK_RESULT(result);
     }
+    result = Dart_SetEnvironmentCallback(EnvironmentCallback);
+    CHECK_RESULT(result);
     Dart_ExitScope();
     Dart_ExitIsolate();
     return isolate;