IndexedDB: Rely on bindings for enum validation

Source/modules/indexeddb/IDBDatabase.cpp

Index: Source/modules/indexeddb/IDBDatabase.cpp
diff --git a/Source/modules/indexeddb/IDBDatabase.cpp b/Source/modules/indexeddb/IDBDatabase.cpp
index 33270b39a61ae2b6637264dcb07b59fb25a580e1..d365d959afae1069d25fc9ad5a2c98841e6b0420 100644
--- a/Source/modules/indexeddb/IDBDatabase.cpp
+++ b/Source/modules/indexeddb/IDBDatabase.cpp
@@ -289,7 +289,12 @@ IDBTransaction* IDBDatabase::transaction(ScriptState* scriptState, const StringO
         return nullptr;
     }
 
-    WebIDBTransactionMode mode = IDBTransaction::stringToMode(modeString, exceptionState);
+    WebIDBTransactionMode mode = IDBTransaction::stringToMode(modeString);
+    if (mode != WebIDBTransactionModeReadOnly && mode != WebIDBTransactionModeReadWrite) {
+        exceptionState.throwTypeError("The mode provided ('" + modeString + "') is not one of 'readonly' or 'readwrite'.");
+        return nullptr;
+    }
+
     if (exceptionState.hadException())
         return nullptr;