Turn WorkerLoaderProxy into a threadsafe, ref-counted object.

Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationNode.idl',
@@ skipping 1960 matching lines @@
             'workers/WorkerConsole.h',
             'workers/WorkerEventQueue.cpp',
             'workers/WorkerEventQueue.h',
             'workers/WorkerGlobalScope.cpp',
             'workers/WorkerGlobalScope.h',
             'workers/WorkerGlobalScopeProxy.h',
             'workers/WorkerGlobalScopeProxyProvider.cpp',
             'workers/WorkerGlobalScopeProxyProvider.h',
             'workers/WorkerInspectorProxy.cpp',
             'workers/WorkerInspectorProxy.h',
+            'workers/WorkerLoaderProxy.cpp',
             'workers/WorkerLoaderProxy.h',
             'workers/WorkerLocation.h',
             'workers/WorkerMessagingProxy.cpp',
             'workers/WorkerMessagingProxy.h',
             'workers/WorkerNavigator.cpp',
             'workers/WorkerNavigator.h',
             'workers/WorkerObjectProxy.cpp',
             'workers/WorkerObjectProxy.h',
             'workers/WorkerReportingProxy.h',
             'workers/WorkerScriptLoader.cpp',
@@ skipping 1776 matching lines @@
             'rendering/style/SVGRenderStyleTest.cpp',
             'streams/ExclusiveStreamReaderTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'testing/UnitTestHelpers.cpp',
             'testing/UnitTestHelpers.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }