Remove some hacks in the testing scripts & prepare for checked mode handling with kernel

tools/testing/dart/runtime_configuration.dart

Index: tools/testing/dart/runtime_configuration.dart
diff --git a/tools/testing/dart/runtime_configuration.dart b/tools/testing/dart/runtime_configuration.dart
index 5fb10072938cea0a8d36607266846cfc408e2569..8ce994722c69ca4b050132158d76fb1136f2da94 100644
--- a/tools/testing/dart/runtime_configuration.dart
+++ b/tools/testing/dart/runtime_configuration.dart
@@ -280,17 +280,9 @@ class DartPrecompiledRuntimeConfiguration extends DartVmRuntimeConfiguration {
       throw "dart_precompiled cannot run files of type '$type'.";
     }
 
-    var args = new List();
-    args.addAll(arguments);
-    for (var i = 0; i < args.length; i++) {
-      if (args[i].endsWith(".dart")) {
-        args[i] = "${artifact.filename}/out.aotsnapshot";
-      }
-    }
-
     return <Command>[
       commandBuilder.getVmCommand(suite.dartPrecompiledBinaryFileName,
-          args, environmentOverrides)
+          arguments, environmentOverrides)
     ];
   }
 }