Rename DatabaseTaskSynchronizer to TaskSynchronizer and move it to platform/

Source/platform/blink_platform.gypi

 {
   'variables': {
     'platform_files': [
       'AsyncFileSystemCallbacks.h',
       'CalculationValue.cpp',
       'CalculationValue.h',
       'CheckedInt.h',
       'Clock.cpp',
       'Clock.h',
       'ColorChooser.cpp',
@@ skipping 108 matching lines @@
       'SerializedResource.h',
       'SharedBuffer.cpp',
       'SharedBuffer.h',
       'SharedBufferChunkReader.cpp',
       'SharedBufferChunkReader.h',
       'SharedTimer.cpp',
       'SharedTimer.h',
       'StorageQuotaCallbacks.h',
       'Supplementable.h',
       'Task.h',
+      'TaskSynchronizer.cpp',
+      'TaskSynchronizer.h',
       'ThemeTypes.h',
       'Theme.cpp',
       'Theme.h',
       'ThreadTimers.cpp',
       'ThreadTimers.h',
       'Timer.cpp',
       'Timer.h',
       'TraceEvent.h',
       'UserGestureIndicator.cpp',
       'UserGestureIndicator.h',
@@ skipping 774 matching lines @@
     # NOTE: these are legacy unit tests, do not add more!
     'platform_web_unittest_files': [
       'animation/TimingFunctionTest.cpp',
       'graphics/DeferredImageDecoderTest.cpp',
       'graphics/ImageDecodingStoreTest.cpp',
       'graphics/ImageFrameGeneratorTest.cpp',
       'graphics/test/MockImageDecoder.h',
     ],
   },
 }