Implement 'as' operator.

lib/compiler/implementation/scanner/token.dart

Index: lib/compiler/implementation/scanner/token.dart
diff --git a/lib/compiler/implementation/scanner/token.dart b/lib/compiler/implementation/scanner/token.dart
index ddd921b074745f311777c71ec04380a0e8b2f4a4..280488d1709b8c8102a41977af5d45f94f714662 100644
--- a/lib/compiler/implementation/scanner/token.dart
+++ b/lib/compiler/implementation/scanner/token.dart
@@ -71,6 +71,7 @@ final int PERCENT_EQ_TOKEN = TILDE_SLASH_TOKEN + 1;
 final int GT_GT_TOKEN = PERCENT_EQ_TOKEN + 1;
 final int CARET_EQ_TOKEN = GT_GT_TOKEN + 1;
 final int IS_TOKEN = CARET_EQ_TOKEN + 1;
+final int AS_TOKEN = IS_TOKEN + 1;
 
 // TODO(ahe): Get rid of this.
 final int UNKNOWN_TOKEN = 1024;
@@ -360,6 +361,8 @@ final PrecedenceInfo GT_INFO =
   const PrecedenceInfo(const SourceString('>'), 10, GT_TOKEN);
 final PrecedenceInfo IS_INFO =
   const PrecedenceInfo(const SourceString('is'), 10, IS_TOKEN);
+final PrecedenceInfo AS_INFO =
+  const PrecedenceInfo(const SourceString('as'), 10, AS_TOKEN);
 final PrecedenceInfo LT_EQ_INFO =
   const PrecedenceInfo(const SourceString('<='), 10, LT_EQ_TOKEN);
 final PrecedenceInfo LT_INFO =