Use random debug port in basic_debugger_test.

tests/standalone/debugger/debug_lib.dart

Index: tests/standalone/debugger/debug_lib.dart
===================================================================
--- tests/standalone/debugger/debug_lib.dart	(revision 20550)
+++ tests/standalone/debugger/debug_lib.dart	(working copy)
@@ -10,10 +10,6 @@
 import "dart:utf";
 import "dart:json" as JSON;
 
-// TODO(hausner): need to select a different port number for each
-// test that runs in parallel.
-var debugPort = 5860;
-
 // Whether or not to print debug target process on the console.
 var showDebuggeeOutput = true;
 
@@ -498,14 +494,12 @@
       print("Target process killed");
     }
     Expect.isTrue(!errorsDetected);
-    stdin.close();
-    stdout.close();
-    stderr.close();
+    exit(errors.length);
   }
 }
 
 
-bool RunScript(List script) {
+bool RunScript(List script, int debugPort) {
   var options = new Options();
   if (options.arguments.contains("--debuggee")) {
     return false;