Introduce .isMalformed

pkg/compiler/lib/src/resolution/signatures.dart

Index: pkg/compiler/lib/src/resolution/signatures.dart
diff --git a/pkg/compiler/lib/src/resolution/signatures.dart b/pkg/compiler/lib/src/resolution/signatures.dart
index 41f3033d2555d04b49fe60b912b0f7eb615ebde6..94ebf43b50f4e178aeffddda8cb111bccceba0f8 100644
--- a/pkg/compiler/lib/src/resolution/signatures.dart
+++ b/pkg/compiler/lib/src/resolution/signatures.dart
@@ -310,7 +310,7 @@ class SignatureResolver extends MappingVisitor<FormalElementX> {
     int requiredParameterCount = 0;
     if (formalParameters == null) {
       if (!element.isGetter) {
-        if (element.isErroneous) {
+        if (element.isMalformed) {
           // If the element is erroneous, an error should already have been
           // reported. In the case of parse errors, it is possible that there
           // are formal parameters, but something else in the method failed to