MalformedType used for all invalid type annotations.

sdk/lib/_internal/compiler/implementation/lib/js_helper.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
index b93f71a7c0bbbfd00d438e08bae262fd3becc8e0..7ed7b2d1177b7f4d399b8e8f7091a6e8fdaf45ea 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_helper.dart
@@ -538,7 +538,7 @@ class Primitives {
   static num numMicroseconds() {
     if (JS('bool', 'typeof window != "undefined" && window !== null')) {
       var performance = JS('var', 'window.performance');
-      if (performance != null && 
+      if (performance != null &&
           JS('bool', 'typeof #.webkitNow == "function"', performance)) {
         return (1000 * JS('num', '#.webkitNow()', performance)).floor();
       }
@@ -961,6 +961,14 @@ throwRuntimeError(message) {
   throw new RuntimeError(message);
 }
 
+/**
+ * The SSA builder generates a call to this method when a malformed type is used
+ * in a subtype test.
+ */
+throwMalformedSubtypeError(value, type, reasons) {
+  throw new TypeErrorImplementation.malformedSubtype(value, type, reasons);
+}
+
 throwAbstractClassInstantiationError(className) {
   throw new AbstractClassInstantiationError(className);
 }
@@ -1519,6 +1527,11 @@ voidTypeCheck(value) {
   throw new TypeErrorImplementation(value, 'void');
 }
 
+malformedTypeCheck(value, type, reasons) {
+  if (value == null) return value;
+  throwMalformedSubtypeError(value, type, reasons);
+}
+
 /**
  * Special interface recognized by the compiler and implemented by DOM
  * objects that support integer indexing. This interface is not
@@ -1533,9 +1546,22 @@ abstract class JavaScriptIndexingBehavior {
 /** Thrown by type assertions that fail. */
 class TypeErrorImplementation implements TypeError {
   final String message;
+
+  /**
+   * Normal type error caused by a failed subtype test.
+   */
   TypeErrorImplementation(Object value, String type)
-    : message = "type '${Primitives.objectTypeName(value)}' is not a subtype "
-                "of type '$type'";
+      : message = "type '${Primitives.objectTypeName(value)}' is not a subtype "
+                  "of type '$type'";
+
+  /**
+   * Type error caused by a subtype test on a malformed type.
+   */
+  TypeErrorImplementation.malformedSubtype(Object value,
+                                           String type, String reasons)
+      : message = "type '${Primitives.objectTypeName(value)}' is not a subtype "
+                  "of type '$type' because '$type' is malformed: $reasons.";
+
   String toString() => message;
 }