Add StackTrace.current getter.

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
@@ skipping 13 matching lines @@
    *
    * The `stackTraceString` can be a string returned by some other
    * stack trace, or it can be any string at all.
    * If the string doesn't look like a stack trace, code that interprets
    * stack traces is likely to fail, so fake stack traces should be used
    * with care.
    */
   factory StackTrace.fromString(String stackTraceString) = _StringStackTrace;
 
   /**
+   * Returns a representation of the current stack trace.
+   *
+   * This is similar to what can be achieved by doing:
+   *
+   *     try { throw 0; } catch (_, stack) { return stack; }
+   *
+   * The getter achieves this without throwing, except on platforms that
+   * have no other way to get a stack trace.
+   */
+  external static StackTrace get current;
+
+  /**
    * Returns a [String] representation of the stack trace.
    *
    * The string represents the full stack trace starting from
    * the point where a throw ocurred to the top of the current call sequence.
    *
    * The exact format of the string representation is not final.
    */
   String toString();
 }
 
 class _StringStackTrace implements StackTrace {
   final String _stackTrace;
   _StringStackTrace(this._stackTrace);
   String toString() => _stackTrace;
 }