Remove support for 'argument definitions test' from dart2js.

sdk/lib/_internal/compiler/implementation/scanner/parser.dart

Index: sdk/lib/_internal/compiler/implementation/scanner/parser.dart
diff --git a/sdk/lib/_internal/compiler/implementation/scanner/parser.dart b/sdk/lib/_internal/compiler/implementation/scanner/parser.dart
index 7708cac7bb33bcfcaa409aa9fa43baa4930667dd..78329cc69568c1936b775f8146d918dcdf596977 100644
--- a/sdk/lib/_internal/compiler/implementation/scanner/parser.dart
+++ b/sdk/lib/_internal/compiler/implementation/scanner/parser.dart
@@ -1531,22 +1531,11 @@ class Parser {
                (identical(kind, OPEN_CURLY_BRACKET_TOKEN)) ||
                identical(token.stringValue, '[]')) {
       return parseLiteralListOrMap(token);
-    } else if (identical(kind, QUESTION_TOKEN)) {
-      return parseArgumentDefinitionTest(token);
     } else {
       return listener.expectedExpression(token);
     }
   }
 
-  Token parseArgumentDefinitionTest(Token token) {
-    Token questionToken = token;
-    listener.beginArgumentDefinitionTest(questionToken);
-    assert(optional('?', token));
-    token = parseIdentifier(token.next);
-    listener.endArgumentDefinitionTest(questionToken, token);
-    return token;
-  }
-
   Token parseParenthesizedExpressionOrFunctionLiteral(Token token) {
     BeginGroupToken beginGroup = token;
     int kind = beginGroup.endGroup.next.kind;