Refactor TimeBase to post tasks. Workers to use real Idle tasks.

Source/platform/blink_platform.gypi

 {
   'includes': [
     'platform_generated.gypi',
   ],
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
@@ skipping 75 matching lines @@
       'PlatformGestureEvent.h',
       'PlatformInstrumentation.cpp',
       'PlatformInstrumentation.h',
       'PlatformKeyboardEvent.cpp',
       'PlatformKeyboardEvent.h',
       'PlatformMouseEvent.h',
       'PlatformResourceLoader.cpp',
       'PlatformResourceLoader.h',
       'PlatformScreen.cpp',
       'PlatformScreen.h',
-      'PlatformThreadData.cpp',
-      'PlatformThreadData.h',
       'PlatformTouchEvent.h',
       'PlatformTouchPoint.h',
       'PlatformWheelEvent.h',
       'PopupMenu.h',
       'PopupMenuStyle.h',
       'Prerender.cpp',
       'Prerender.h',
       'PrerenderClient.h',
       'PurgeableVector.cpp',
       'PurgeableVector.h',
@@ skipping 10 matching lines @@
       'SharedTimer.cpp',
       'SharedTimer.h',
       'StorageQuotaCallbacks.h',
       'Supplementable.h',
       'Task.h',
       'TaskSynchronizer.cpp',
       'TaskSynchronizer.h',
       'Theme.cpp',
       'Theme.h',
       'ThemeTypes.h',
-      'ThreadTimers.cpp',
-      'ThreadTimers.h',
       'Timer.cpp',
       'Timer.h',
       'TraceEvent.h',
       'TracedValue.cpp',
       'TracedValue.h',
       'URLPatternMatcher.cpp',
       'URLPatternMatcher.h',
       'UUID.cpp',
       'UUID.h',
       'UserGestureIndicator.cpp',
@@ skipping 846 matching lines @@
       'graphics/ImageLayerChromiumTest.cpp',
       'graphics/test/MockImageDecoder.h',
       'graphics/test/MockWebGraphicsContext3D.h',
       'image-decoders/bmp/BMPImageDecoderTest.cpp',
       'image-decoders/gif/GIFImageDecoderTest.cpp',
       'image-decoders/jpeg/JPEGImageDecoderTest.cpp',
       'image-decoders/webp/WEBPImageDecoderTest.cpp',
     ],
   },
 }