Add a debugger test for closure breakpoints

tests/standalone/debugger/closure_debugger_test.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// This test forks a second vm process that runs this dart script as
+// a debug target.
+// Run this test with option --wire to see the json messages sent
+// between the processes.
+// Run this test with option --verbose to see the stdout and stderr output
+// of the debug target process.
+
+import "debug_lib.dart";
+
+bar(x) {
+  print(x);
+}
+
+main() {
+  if (RunScript(testScript)) return;
+  print("Hello from debuggee");
+  var f = bar;
+  f("closure call");
+  bar(12);
+}
+
+
+// Expected debugger events and commands.
+var testScript = [
+  MatchFrame(0, "main"),  // Top frame in trace is function "main".
+  SetBreakpoint(22),      // Set breakpoint a line 22, at the closure call.
+  Resume(),
+  MatchFrame(0, "main"),  // Should be at closure call.
+  StepInto(),
+  MatchFrames(["bar", "main"]),  // Should be in closure function now.
+  StepOut(),
+  MatchFrame(0, "main"),  // Back in main, before static call to bar().
+  SetBreakpoint(15),      // Breakpoint in bar();

[siva, 2013/05/10 22:02:58]

Maybe SetBreakpoint("bar") would be more readable and less prone to errors if
somebody decides to do a mass change of the copyright text.

Similarly 'Step, Step, Step, Step'  instead of SetBreakpoint(22) or have another
top level function whose first statement is the closure call.

[hausner, 2013/05/16 16:32:39]

As discussed offline, this is certainly brittle code but unfortunately there is
no solution that is significantly more robust. Ideal would be if a dart program
could get access to its source file and we could put a unique comment in the
line where we want to set a breakpoint.

On 2013/05/10 22:02:58, siva wrote:

+  Resume(),
+  MatchFrames(["bar", "main"]),
+  Resume(),
+];