VM: Fix issue with local variable values reported by the debugger.

tests/standalone/debugger/local_variables_test.dart

+// Copyright (c) 2015, 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";
+
+foo() {
+  var y;  // Breakpoint
+  return 123;
+}
+
+test() {
+  if (true) {
+    var temp = 777;
+  }
+  if (true) {
+    var a = foo();  // Breakpoint
+    if (true) {
+      var s = 456;
+      print(s);
+    }
+  }
+}
+
+main(List<String> arguments) {
+  if (RunScript(testScript, arguments)) return;
+  print("Hello from debuggee");
+  test();
+  print("Hello again");
+}
+
+
+// Expected debugger events and commands.
+var testScript = [
+  MatchFrame(0, "main"),  // Top frame in trace is function "main".
+  Step(),
+  MatchFrame(0, "main"),  // Should still be in "main".
+  SetBreakpoint(15),  // Set breakpoint in function foo.
+  SetBreakpoint(24),  // Set breakpoint in function test.
+  Resume(),
+  MatchFrames(["test", "main"]),
+  AssertLocalsNotVisible(["a"]),  // Here, a is not in scope yet.
+  Resume(),
+  MatchFrames(["foo", "test", "main"]),
+  AssertLocalsNotVisible(["a"], 1),  // In the caller, a is not in scope.
+  Step(),
+  MatchLocals({"y": "null"}),  // Expect y initialized to null.
+  Resume(),
+];