- Revert r24441 until issues found have been addressed.

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 24442)
+++ runtime/vm/parser.cc	(working copy)
@@ -9830,6 +9830,8 @@
     } else {
       primary = new PrimaryNode(TokenPos(), Symbols::Super());
     }
+  } else if (CurrentToken() == Token::kCONDITIONAL) {
+    primary = ParseArgumentDefinitionTest();
   } else {
     UnexpectedToken();
   }
@@ -10029,6 +10031,12 @@
     case Token::kINDEX:
       SkipCompoundLiteral();
       break;
+    case Token::kCONDITIONAL:
+      ConsumeToken();
+      if (IsIdentifier()) {
+        ConsumeToken();
+      }
+      break;
     default:
       if (IsIdentifier()) {
         ConsumeToken();  // Handle pseudo-keyword identifiers.