Add missing traces for Supplement<> classes

third_party/WebKit/Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/KeyframeEffect.idl',
             'animation/EffectModel.idl',
             'animation/AnimationEffectReadOnly.idl',
@@ skipping 2253 matching lines @@
             'workers/SharedWorker.h',
             'workers/SharedWorkerGlobalScope.cpp',
             'workers/SharedWorkerGlobalScope.h',
             'workers/SharedWorkerRepositoryClient.h',
             'workers/SharedWorkerThread.cpp',
             'workers/SharedWorkerThread.h',
             'workers/Worker.cpp',
             'workers/Worker.h',
             'workers/WorkerBackingThread.cpp',
             'workers/WorkerBackingThread.h',
+            'workers/WorkerClients.cpp',
             'workers/WorkerClients.h',
             'workers/WorkerEventQueue.cpp',
             'workers/WorkerEventQueue.h',
             'workers/WorkerGlobalScope.cpp',
             'workers/WorkerGlobalScope.h',
             'workers/WorkerInspectorProxy.cpp',
             'workers/WorkerInspectorProxy.h',
             'workers/WorkerLoaderProxy.cpp',
             'workers/WorkerLoaderProxy.h',
             'workers/WorkerLocation.h',
@@ skipping 1922 matching lines @@
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'timing/PerformanceBaseTest.cpp',
             'timing/PerformanceObserverTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'workers/WorkerThreadTestHelper.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }