Replace IDBPendingTransactionMonitor with end-of-recursion-scope tasks

Source/modules/modules.gypi

 {
   'includes': [
     '../core/core_generated.gypi',
     'modules_generated.gypi',
   ],
   'variables': {
     # Experimental hooks for embedder to provide extra IDL and source files.
     #
     # Note: this is not a supported API. If you rely on this, you will be broken
     # from time to time as the code generator changes in backward incompatible
@@ skipping 551 matching lines @@
       'indexeddb/IDBKey.h',
       'indexeddb/IDBKeyPath.cpp',
       'indexeddb/IDBKeyPath.h',
       'indexeddb/IDBKeyRange.cpp',
       'indexeddb/IDBKeyRange.h',
       'indexeddb/IDBMetadata.h',
       'indexeddb/IDBObjectStore.cpp',
       'indexeddb/IDBObjectStore.h',
       'indexeddb/IDBOpenDBRequest.cpp',
       'indexeddb/IDBOpenDBRequest.h',
-      'indexeddb/IDBPendingTransactionMonitor.cpp',
-      'indexeddb/IDBPendingTransactionMonitor.h',
       'indexeddb/IDBRequest.cpp',
       'indexeddb/IDBRequest.h',
       'indexeddb/IDBTracing.h',
       'indexeddb/IDBTransaction.cpp',
       'indexeddb/IDBTransaction.h',
       'indexeddb/IDBVersionChangeEvent.cpp',
       'indexeddb/IDBVersionChangeEvent.h',
       'indexeddb/IndexedDB.h',
       'indexeddb/IndexedDBClient.cpp',
       'indexeddb/IndexedDBClient.h',
@@ skipping 471 matching lines @@
       'serviceworkers/CacheTest.cpp',
       'serviceworkers/FetchResponseDataTest.cpp',
       'serviceworkers/RequestTest.cpp',
       'serviceworkers/ResponseTest.cpp',
       'serviceworkers/ServiceWorkerContainerTest.cpp',
       'websockets/DOMWebSocketTest.cpp',
       'websockets/DocumentWebSocketChannelTest.cpp',
     ],
   },
 }