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

tools/testing/dart/test_runner.dart

Index: tools/testing/dart/test_runner.dart
diff --git a/tools/testing/dart/test_runner.dart b/tools/testing/dart/test_runner.dart
index 471e061916d206f02622f83dea7cbc305a80c345..67da176072299c32bcf3d9b3bfc1eec8ea94eb7d 100644
--- a/tools/testing/dart/test_runner.dart
+++ b/tools/testing/dart/test_runner.dart
@@ -2733,18 +2733,10 @@ class CommandExecutorImpl implements CommandExecutor {
           .runAdbCommand(['push', '$testdir/$file', '$deviceTestDir/$file']));
     }
 
-    var args = new List();
-    args.addAll(arguments);
-    for (var i = 0; i < args.length; i++) {
-      if (args[i].endsWith(".dart")) {
-        args[i] = "$deviceTestDir/out.aotsnapshot";
-      }
-    }
-
     steps.add(() => device.runAdbShellCommand(
         [
           '$devicedir/dart_precompiled_runtime',
-        ]..addAll(args),
+        ]..addAll(arguments),
         timeout: timeoutDuration));
 
     var stopwatch = new Stopwatch()..start();