Support new malformed types semantics.

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index 2f9027256c28141316bef0ff9df50c1c58f8176a..76e431bf56d9959d1bdbbea95386204c15fb372a 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -33,7 +33,6 @@ class CheckedModeHelper {
   void generateAdditionalArguments(SsaCodeGenerator codegen,
                                    HTypeConversion node,
                                    List<jsAst.Expression> arguments) {
-    assert(!node.typeExpression.isMalformed);
     // No additional arguments needed.
   }
 }
@@ -45,7 +44,6 @@ class PropertyCheckedModeHelper extends CheckedModeHelper {
                                    HTypeConversion node,
                                    List<jsAst.Expression> arguments) {
     DartType type = node.typeExpression;
-    assert(!type.isMalformed);
     String additionalArgument = codegen.backend.namer.operatorIsType(type);
     arguments.add(js.string(additionalArgument));
   }
@@ -114,8 +112,8 @@ class MalformedCheckedModeHelper extends CheckedModeHelper {
                                    HTypeConversion node,
                                    List<jsAst.Expression> arguments) {
     DartType type = node.typeExpression;
-    assert(type.isMalformed);
-    String reasons = Types.fetchReasonsFromMalformedType(type);
+    assert(type.containsAmbiguousTypes);
+    String reasons = Types.fetchReasonsFromAmbiguousType(type);
     arguments.add(js.string('$type'));
     // TODO(johnniwinther): Handle escaping correctly.
     arguments.add(js.string(reasons));
@@ -807,11 +805,11 @@ class JavaScriptBackend extends Backend {
       // We also need the native variant of the check (for DOM types).
       helper = getNativeCheckedModeHelper(type, typeCast: false);
       if (helper != null) world.addToWorkList(helper.getElement(compiler));
-      if (type.isMalformed) {
+      if (type.containsAmbiguousTypes) {
         enqueueInResolution(getThrowMalformedSubtypeError(), elements);
         return;
       }
-    } else if (type.isMalformed) {
+    } else if (type.containsAmbiguousTypes) {
       registerThrowRuntimeError(elements);
       return;
     }
@@ -1074,7 +1072,7 @@ class JavaScriptBackend extends Backend {
     Element element = type.element;
     bool nativeCheck = nativeCheckOnly ||
         emitter.nativeEmitter.requiresNativeIsCheck(element);
-    if (type.isMalformed) {
+    if (type.containsAmbiguousTypes) {
       // Check for malformed types first, because the type may be a list type
       // with a malformed argument type.
       if (nativeCheckOnly) return null;