Add functionality to get full stack trace when exceptions are thrown.

sdk/lib/core/stacktrace.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.
+
+part of dart.core;
+
+/**
+ * An interface implemented by all stack trace objects.
+ *
+ * A [StackTrace] is intended to convey information to the user about the call
+ * sequence that triggered an exception.
+ *
+ * These objects are created by the runtime, it is not possible to create
+ * them programmatically.
+ */
+abstract class StackTrace {
+  // Returns a String object that contains the full stack trace starting from
+  // the point where an exception has ocurred to the entry function which is
+  // typically 'main'.
+  // 'toString()' on a stack trace object essentially invokes this getter.
+  external String get fullStackTrace;
+
+  // Returns a String object that contains a stack trace starting from the
+  // point where an exception has ocurred to the point where the exception
+  // is caught.
+  external String get stackTrace;
+}
+