Implementation of async-await transformation on js ast.

pkg/compiler/lib/src/js/printer.dart

 // Copyright (c) 2012, 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 js;
 
 class Printer extends Indentation implements NodeVisitor {
   final bool shouldCompressOutput;
   leg.DiagnosticListener diagnosticListener;
   CodeBuffer outBuffer;
@@ skipping 337 matching lines @@
       outIndent("return");
     } else {
       outIndent("return");
       pendingSpace = true;
       visitNestedExpression(node.value, EXPRESSION,
                             newInForInit: false, newAtStatementBegin: false);
     }
     outSemicolonLn();
   }
 
+  visitYield(Yield node) {
+    if (node.hasStar) {
+      outIndent("yield*");
+    } else {
+      outIndent("yield");
+    }
+    pendingSpace = true;
+    visitNestedExpression(node.expression, EXPRESSION,
+                          newInForInit: false, newAtStatementBegin: false);
+    outSemicolonLn();
+  }
+
+
   visitThrow(Throw node) {
     outIndent("throw");
     pendingSpace = true;
     visitNestedExpression(node.expression, EXPRESSION,
                           newInForInit: false, newAtStatementBegin: false);
     outSemicolonLn();
   }
 
   visitTry(Try node) {
     outIndent("try");
@@ skipping 821 matching lines @@
         codes.add(nthLetter((n ~/ nameSpaceSize) % LETTERS));
       }
       codes.add(charCodes.$0 + digit);
       newName = new String.fromCharCodes(codes);
     }
     assert(new RegExp(r'[a-zA-Z][a-zA-Z0-9]*').hasMatch(newName));
     maps.last[oldName] = newName;
     return newName;
   }
 }