Bug 1636285: Add a descriptive message to EnsureJNIObject; r=geckoview-reviewers,droeh

Differential Revision: https://phabricator.services.mozilla.com/D74328

widget/android/jni/Utils.cpp

@@ -254,7 +254,8 @@ bool EnsureJNIObject(JNIEnv* env, jobject instance) {
     sJNIObjectHandleField = env->GetFieldID(sJNIObjectClass, "mHandle", "J");
   }
 
-  MOZ_ASSERT(env->IsInstanceOf(instance, sJNIObjectClass));
+  MOZ_ASSERT(env->IsInstanceOf(instance, sJNIObjectClass),
+             "Java class is not derived from JNIObject");
   return true;
 }