Incremental parser fix: handle insertion of method parameters.

pkg/analyzer/lib/src/generated/parser.dart

Index: pkg/analyzer/lib/src/generated/parser.dart
diff --git a/pkg/analyzer/lib/src/generated/parser.dart b/pkg/analyzer/lib/src/generated/parser.dart
index 45a62e3a85f1480e523d5a5d20eb4de97379358d..7bd33af428fde76589e8a979fb219916cf2fada5 100644
--- a/pkg/analyzer/lib/src/generated/parser.dart
+++ b/pkg/analyzer/lib/src/generated/parser.dart
@@ -1388,6 +1388,11 @@ class IncrementalParseDispatcher implements AstVisitor<AstNode> {
     } else if (identical(_oldNode, node.body)) {
       //return parser.parseFunctionBody();
       throw new InsufficientContextException();
+    } else if (identical(_oldNode, node.parameters)) {
+      // TODO(paulberry): if we want errors to be correct, we'll need to also
+      // call _validateFormalParameterList, and sometimes
+      // _validateModifiersForGetterOrSetterOrMethod.
+      return _parser.parseFormalParameterList();
     }
     return _notAChild(node);
   }