Initialize TokenizerBase int fields for better dart2js codegen.

This change removes ~15k of needless receiver type checks from csslib due to inferred null values.

BUG=
R=terry@google.com

Review URL: https://codereview.chromium.org//679773003

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/csslib@41295 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/lib/src/tokenizer_base.dart b/lib/src/tokenizer_base.dart
index 07dee48..5501e6c 100644
--- a/lib/src/tokenizer_base.dart
+++ b/lib/src/tokenizer_base.dart
@@ -52,8 +52,8 @@
   //     http://dev.w3.org/csswg/selectors4/
   bool inSelector = false;
 
-  int _index;
-  int _startIndex;
+  int _index = 0;
+  int _startIndex = 0;
 
   static const String _CDATA_START = '<![CDATA[';
   static const String _CDATA_END = ']]>';
@@ -435,4 +435,3 @@
     }
   }
 }
-