Better casting of for-in loops.

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

Index: pkg/analyzer/lib/src/generated/error_verifier.dart
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index efd0f9365e26ac40b9008164b1c7000bef503189..28d02ec10a1ef67e12193db4bc039cffb3dc0b16 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -5694,6 +5694,15 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
     iterableType = iterableType.resolveToBound(_typeProvider.objectType);
     DartType bestIterableType =
         _typeSystem.mostSpecificTypeArgument(iterableType, loopType);
+
+    // Allow it to be a supertype of Iterable<T> (basically just Object) and do
+    // an implicit downcast to Iterable<dynamic>.
+    if (bestIterableType == null) {
+      if (_typeSystem.isSubtypeOf(loopType, iterableType)) {
+        bestIterableType = DynamicTypeImpl.instance;
+      }
+    }
+
     if (bestIterableType == null) {
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.FOR_IN_OF_INVALID_TYPE,