message: remove unneccesary type casts
diff: @@ -294,7 +294,7 @@ class DocumentConverter {
  const namespaceName = namespace.join('.');
  if (this.isNamespace(statement) && value.type === 'ObjectExpression') {
  - this.rewriteNamespaceObject(namespaceName, value as ObjectExpression, statement);
  + this.rewriteNamespaceObject(namespaceName, value, statement);
  } else if (value.type === 'Identifier') {
  // An 'export' of the form:
  // Polymer.Foo = Foo;
  @@ -540,7 +540,7 @@ class DocumentConverter {
  * @param statement the statement, to be replaced, that contains the namespace
  */
  rewriteNamespaceObject(name: string, body: ObjectExpression, statement: Statement) {
  - const exports = getNamespaceExports(body as ObjectExpression);
  + const exports = getNamespaceExports(body);
  // Replace original namespace statement with new exports
  const nsIndex = this.program.body.indexOf(statement);
  