Report error in APIs if type is malformed instead of crashing. Example:

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2012, 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.
 
 #include "include/dart_api.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart.h"
@@ skipping 271 matching lines @@
   }
   return false;
 }
 
 
 // When we want to return a handle to a type to the user, we handle
 // class-types differently than some other types.
 static Dart_Handle TypeToHandle(Isolate* isolate,
                                 const char* function_name,
                                 const AbstractType& type) {
-  if (type.HasResolvedTypeClass()) {
+  if (type.IsMalformed()) {
+    const Error& error = Error::Handle(type.malformed_error());
+    return Api::NewError("%s: malformed type encountered: %s.",
+        function_name, error.ToErrorCString());
+  } else if (type.HasResolvedTypeClass()) {
     const Class& cls = Class::Handle(isolate, type.type_class());
 #if defined(DEBUG)
     const Library& lib = Library::Handle(cls.library());
     if (lib.IsNull()) {
       ASSERT(cls.IsDynamicClass() || cls.IsVoidClass());
     }
 #endif
     return Api::NewHandle(isolate, cls.raw());
   } else if (type.IsTypeParameter()) {
     return Api::NewHandle(isolate, type.raw());
@@ skipping 4188 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success(isolate);
 }
 
 }  // namespace dart