[analyzer/ffi] Fix crash with dynamic field in struct

Closes: #38993

Change-Id: I6aaa265020709d5846a40bd8fb1c7bd1ef38903c
Cq-Include-Trybots: luci.dart.try:vm-ffi-android-debug-arm-try,vm-ffi-android-debug-arm64-try,dart-sdk-linux-try,analyzer-analysis-server-linux-try,analyzer-linux-release-try,front-end-linux-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/122341
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

Author: dcharkes

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

@@ -141,7 +141,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
       element.name == 'DynamicLibrary' && element.library.name == 'dart.ffi';
 
   /// Return `true` if the given [element] represents the class `Pointer`.
-  bool _isPointer(ClassElement element) =>
+  bool _isPointer(Element element) =>
       element.name == 'Pointer' && element.library.name == 'dart.ffi';
 
   /// Return `true` if the [typeName] represents a subtype of `Struct`.

tests/ffi/regress_38993_test.dart

@@ -0,0 +1,13 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// Tests a compile time error that should not crash the analyzer or CFE.
+
+import "dart:ffi";
+
+class C extends Struct {
+  dynamic x; //# 1: compile-time error
+}
+
+main() {}