dart2js: Use frequency of occurence to sort metadata indices.

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

 // 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.
 
 library rewrite_async;
 
 import "dart:math" show max;
 import 'dart:collection';
 
 import 'package:_internal/compiler/js_lib/shared/async_await_error_codes.dart'
@@ skipping 1165 matching lines @@
   @override
   js.Expression visitLiteralNumber(js.LiteralNumber node) => node;
 
   @override
   visitLiteralStatement(js.LiteralStatement node) => unsupported(node);
 
   @override
   js.Expression visitLiteralString(js.LiteralString node) => node;
 
   @override
+  js.Expression visitStringConcatenation(js.StringConcatenation node) => node;
+
+  @override
   visitNamedFunction(js.NamedFunction node) {
     unsupported(node);
   }
 
   @override
+  js.Expression visitTokenExpression(js.TokenExpression node) => node;
+
+  @override
+  js.Expression visitTokenNumber(js.TokenNumber node) => node;
+
+  @override
+  js.Expression visitTokenString(js.TokenString node) => node;
+
+  @override
   js.Expression visitNew(js.New node) {
     bool storeTarget = node.arguments.any(shouldTransform);
     return withCallTargetExpression(node.target, (target) {
       return withExpressions(node.arguments, (List<js.Expression> arguments) {
         return new js.New(target, arguments);
       });
     }, store: storeTarget);
   }
 
   @override
@@ skipping 1177 matching lines @@
   @override
   bool visitLabeledStatement(js.LabeledStatement node) {
     usedNames.add(node.label);
     labelledStatements.add(node);
     bool containsAwait = visit(node.body);
     labelledStatements.removeLast();
     return containsAwait;
   }
 
   @override
+  bool visitTokenExpression(js.TokenExpression node) {
+    return false;
+  }
+
+  @override
+  bool visitTokenNumber(js.TokenNumber node) {
+    return false;
+  }
+
+  @override
+  bool visitTokenString(js.TokenString node) {
+    return false;
+  }
+
+  @override
   bool visitLiteralBool(js.LiteralBool node) {
     return false;
   }
 
   @override
   bool visitLiteralExpression(js.LiteralExpression node) {
     return unsupported(node);
   }
 
   @override
@@ skipping 10 matching lines @@
   bool visitLiteralStatement(js.LiteralStatement node) {
     return unsupported(node);
   }
 
   @override
   bool visitLiteralString(js.LiteralString node) {
     return false;
   }
 
   @override
+  bool visitStringConcatenation(js.StringConcatenation node) {
+    return true;
+  }
+
+
+  @override
   bool visitNamedFunction(js.NamedFunction node) {
     return false;
   }
 
   @override
   bool visitNew(js.New node) {
     return visitCall(node);
   }
 
   @override
@@ skipping 114 matching lines @@
     return condition || body;
   }
 
   @override
   bool visitDartYield(js.DartYield node) {
     hasYield = true;
     visit(node.expression);
     return true;
   }
 }