support class native clause

pkg/front_end/lib/src/fasta/parser/parser.dart

Index: pkg/front_end/lib/src/fasta/parser/parser.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/parser.dart b/pkg/front_end/lib/src/fasta/parser/parser.dart
index f7e2e1f90c1ca2e2ecc07d131512ef7aaa3a7661..365b7979d7573c7375bccbbc8cb521435273c237 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -857,9 +857,14 @@ class Parser {
         ++interfacesCount;
       } while (optional(',', token));
     }
+    Token nativeToken;
+    if (optional('native', token)) {
+      nativeToken = token;
+      token = parseNativeClause(nativeToken);
+    }
     token = parseClassBody(token);
     listener.endClassDeclaration(interfacesCount, begin, classKeyword,
-        extendsKeyword, implementsKeyword, token);
+        extendsKeyword, implementsKeyword, nativeToken, token);
     return token.next;
   }
 
@@ -2105,6 +2110,19 @@ class Parser {
     return token;
   }
 
+  Token parseNativeClause(Token nativeToken) {
+    Token token = nativeToken.next;
+    bool hasName = false;
+    if (token.kind == STRING_TOKEN) {
+      hasName = true;
+      token = parseLiteralString(token);
+    }
+    listener.handleNativeClause(nativeToken, hasName);
+    reportRecoverableError(
+        nativeToken, fasta.messageNativeClauseShouldBeAnnotation);
+    return token;
+  }
+
   Token skipClassBody(Token token) {
     if (!optional('{', token)) {
       return reportUnrecoverableErrorWithToken(