Offer User Timing in workers

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 1983 matching lines @@
             'streams/Stream.cpp',
             'streams/Stream.h',
             'streams/UnderlyingSource.h',
             'timing/ConsoleMemory.cpp',
             'timing/ConsoleMemory.h',
             'timing/DOMWindowPerformance.cpp',
             'timing/DOMWindowPerformance.h',
             'timing/MemoryInfo.cpp',
             'timing/Performance.cpp',
             'timing/Performance.h',
+            'timing/PerformanceBase.cpp',
+            'timing/PerformanceBase.h',
             'timing/PerformanceCompositeTiming.cpp',
             'timing/PerformanceCompositeTiming.h',
             'timing/PerformanceEntry.cpp',
             'timing/PerformanceEntry.h',
             'timing/PerformanceMark.h',
             'timing/PerformanceMeasure.h',
             'timing/PerformanceNavigation.cpp',
             'timing/PerformanceNavigation.h',
             'timing/PerformanceRenderTiming.cpp',
             'timing/PerformanceRenderTiming.h',
@@ skipping 1906 matching lines @@
             'style/ComputedStyleTest.cpp',
             'style/OutlineValueTest.cpp',
             'style/SVGComputedStyleTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }