fix #29228, let* precedence should match generated expression

pkg/dev_compiler/lib/src/compiler/code_generator.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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 346 matching lines @@
   }
 
   JS.ObjectInitializer _librariesDebuggerObject() {
     var properties = <JS.Property>[];
     _libraries.forEach((library, value) {
       // TODO(jacobr): we could specify a short library name instead of the
       // full library uri if we wanted to save space.
       properties.add(new JS.Property(
           js.string(jsLibraryDebuggerName(_libraryRoot, library)), value));
     });
-    return new JS.ObjectInitializer(properties);
+    return new JS.ObjectInitializer(properties, multiline: true);
   }
 
   List<String> _getJSName(Element e) {
     if (e.library == null ||
         findAnnotation(e.library, isPublicJSAnnotation) == null) {
       return null;
     }
 
     var libraryJSName = getAnnotationName(e.library, isPublicJSAnnotation);
     var libraryPrefix = <String>[];
@@ skipping 5657 matching lines @@
   if (targetIdentifier.staticElement is! PrefixElement) return false;
   var prefix = targetIdentifier.staticElement as PrefixElement;
 
   // The library the prefix is referring to must come from a deferred import.
   var containingLibrary = resolutionMap
       .elementDeclaredByCompilationUnit(target.root as CompilationUnit)
       .library;
   var imports = containingLibrary.getImportsWithPrefix(prefix);
   return imports.length == 1 && imports[0].isDeferred;
 }