Fix breaking change from next SDK

lib/src/analyzer.dart

 // Copyright (c) 2013, 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 the template compilation that concerns with extracting information
  * from the HTML parse tree.
  */
 library analyzer;
 
-import 'package:csslib/parser.dart' as Css;
+import 'package:csslib/parser.dart' as css;
 import 'package:csslib/visitor.dart' show StyleSheet, treeToDebugString, Visitor, Expressions, VarDefinition;
 import 'package:html5lib/dom.dart';
 import 'package:html5lib/dom_parsing.dart';
 import 'package:source_maps/span.dart' hide SourceFile;
 
 import 'dart_parser.dart';
 import 'files.dart';
 import 'html_css_fixup.dart';
 import 'html5_utils.dart';
 import 'info.dart';
@@ skipping 1071 matching lines @@
   void normalize() {
     // Remove all var definitions for all style sheets analyzed.
     for (var tree in allStyleSheets) new RemoveVarDefinitions().visitTree(tree);
   }
 
   List<StyleSheet> processVars(var libraryInfo) {
     // Get list of all stylesheet(s) dependencies referenced from this file.
     var styleSheets = _dependencies(libraryInfo).toList();
 
     var errors = [];
-    Css.analyze(styleSheets, errors: errors, options:
+    css.analyze(styleSheets, errors: errors, options:
       [_warningsAsErrors ? '--warnings_as_errors' : '', 'memory']);
 
     // Print errors as warnings.
     for (var e in errors) {
       _messages.warning(e.message, e.span);
     }
 
     // Build list of all var definitions.
     Map varDefs = new Map();
     for (var tree in styleSheets) {
@@ skipping 59 matching lines @@
               }
             }
           }
         }
       }
     }
 
     return seen;
   }
 }