Fixes #254 - Better stacktrace support

lib/runtime/_operations.js

 // 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 library defines runtime operations on objects used by the code
  * generator.
  */
 dart_library.library('dart_runtime/_operations', null, /* Imports */[
 ], /* Lazy Imports */[
   'dart/async',
@@ skipping 251 matching lines @@
     }
     return map;
   }
   exports.map = map;
 
   function assert(condition) {
     if (!condition) errors.throwAssertionError();
   }
   exports.assert = assert;
 
-  function throw_(obj) { throw obj; }
-  exports.throw_ = throw_;
+  let _stack = Symbol('_stack');
 
+  function throw_(obj) {
+    obj[_stack] = new Error();
+    throw obj;
+  }
+  exports.throw = throw_;
+
+  function getError(exception) {
+    return exception[_stack] ? exception[_stack] : exception;
+  }
+
+  // This is a utility function: it is only intended to be called from dev
+  // tools.
+  function stackPrint(exception) {
+    var error = getError(exception);
+    console.log(error.stack ? error.stack : 'No stack trace for: ' + error);
+  }
+  exports.stackPrint = stackPrint;
 
   function stackTrace(exception) {
-    return _js_helper.getTraceFromException(exception);
+    var error = getError(exception);
+    return _js_helper.getTraceFromException(error);
   }
   exports.stackTrace = stackTrace;
 
   let _value = Symbol('_value');
   /**
    * Looks up a sequence of [keys] in [map], recursively, and
    * returns the result. If the value is not found, [valueFn] will be called to
    * add it. For example:
    *
    *     let map = new Map();
@@ skipping 101 matching lines @@
     next() {
       let i = this.dartIterator;
       let done = !i.moveNext();
       return { done: done, value: done ? void 0 : i.current };
     }
   }
   exports.JsIterator = JsIterator;
 
 
 });