Add a scoping object to help block scripting during plugin destruction.

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 75 matching lines @@
       'PlatformInstrumentation.cpp',
       'PlatformInstrumentation.h',
       'PlatformKeyboardEvent.cpp',
       'PlatformKeyboardEvent.h',
       'PlatformMouseEvent.h',
       'PlatformResourceLoader.cpp',
       'PlatformResourceLoader.h',
       'PlatformTouchEvent.h',
       'PlatformTouchPoint.h',
       'PlatformWheelEvent.h',
+      'PluginScriptForbiddenScope.cpp',
+      'PluginScriptForbiddenScope.h',
       'PopupMenu.h',
       'PopupMenuStyle.h',
       'Prerender.cpp',
       'Prerender.h',
       'PrerenderClient.h',
       'PurgeableVector.cpp',
       'PurgeableVector.h',
       'RefCountedSupplement.h',
       'ScriptForbiddenScope.cpp',
       'ScriptForbiddenScope.h',
@@ skipping 923 matching lines @@
       ['os_posix==1 and OS!="mac"',
         {
           'platform_test_files': [
             'text/LocaleICUTest.cpp',
           ],
         }
       ],
     ],
   },
 }