title: Export two library which have same class name
body: <p>I met an error when exporting two libraries. And these libraries have exactly same class name.</p>
  <p>File: <code>A.dart</code></p>
  
  <pre class="lang-dart prettyprint-override"><code>library chrome.A;
  class MyClass {
  ...
  }
  </code></pre>
  <p>File: <code>B.dart</code></p>
  <pre class="lang-dart prettyprint-override"><code>library chrome.B;
  class MyClass {
  ..
  }
  </code></pre>
  <p>File: <code>C.dart</code></p>
  <pre class="lang-dart prettyprint-override"><code>library chrome_app;
  export 'A.dart';
  export 'B.dart';  // HERE!! error message for the element 'MyClass' which is defined in the libraries 'A.dart' and 'B.dart'
  </code></pre>
  <p>Is this the intended result?</p>
  <p>I think <code>A.dart</code> and <code>B.dart</code> has their own namespace so that there should be no error.</p>