First version of PerformanceObserver

Source/bindings/core/v8/custom/custom.gypi

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
     'variables': {
         'bindings_core_v8_custom_files': [
             'V8CSSStyleDeclarationCustom.cpp',
             'V8CustomEventCustom.cpp',
             'V8CustomXPathNSResolver.cpp',
             'V8CustomXPathNSResolver.h',
             'V8DevToolsHostCustom.cpp',
             'V8DocumentCustom.cpp',
             'V8ErrorEventCustom.cpp',
             'V8EventTargetCustom.cpp',
             'V8HTMLAllCollectionCustom.cpp',
             'V8HTMLPlugInElementCustom.cpp',
             'V8InjectedScriptManager.cpp',
             'V8MediaQueryListCustom.cpp',
             'V8MessageChannelCustom.cpp',
             'V8MessageEventCustom.cpp',
             'V8MutationObserverCustom.cpp',
+            'V8PerformanceObserverCustom.cpp',
             'V8PopStateEventCustom.cpp',
             'V8PromiseRejectionEventCustom.cpp',
             'V8WindowCustom.cpp',
             'V8XMLHttpRequestCustom.cpp',
         ],
     },
 }