Convert references to FileSystem & Co. into shared pointers (avoid use after free)

libadblockplus.gyp

 {
   'variables': {
     'have_curl': '<!(python check_curl.py)'
   },
   'includes': ['third_party/v8/build/common.gypi',
                'shell/shell.gyp'],
   'targets': [{
     'target_name': 'libadblockplus',
     'type': '<(library)',
     'include_dirs': [
       'include',
       'third_party/v8/include'
     ],
     'defines': ['FILTER_ENGINE_STUBS=1'],
     'all_dependent_settings': {
       'defines': ['FILTER_ENGINE_STUBS=1']
     },
     'dependencies': ['third_party/v8/tools/gyp/v8.gyp:v8'],
     'sources': [
       'src/AppInfoJsObject.cpp',
       'src/ConsoleJsObject.cpp',
+      'src/DefaultErrorCallback.cpp',
       'src/DefaultFileSystem.cpp',
       'src/ErrorCallback.cpp',
       'src/FileSystemJsObject.cpp',
       'src/FilterEngine.cpp',
       'src/GlobalJsObject.cpp',
       'src/JsEngine.cpp',
       'src/JsValue.cpp',
       'src/Thread.cpp',
       'src/Utils.cpp',
       'src/WebRequestJsObject.cpp',
@@ skipping 81 matching lines @@
       'test/FileSystemJsObject.cpp',
       'test/FilterEngineStubs.cpp',
       'test/GlobalJsObject.cpp',
       'test/JsEngine.cpp',
       'test/JsValue.cpp',
       'test/Thread.cpp',
       'test/WebRequest.cpp'
     ]
   }]
 }