Move Region.cpp/.h to platform/

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'ApplicationCacheHost.cpp',
       'ApplicationCacheHostInternal.h',
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'AutofillPopupMenuClient.cpp',
       'AutofillPopupMenuClient.h',
@@ skipping 282 matching lines @@
       'tests/LinkHighlightTest.cpp',
       'tests/ListenerLeakTest.cpp',
       'tests/MemoryInfo.cpp',
       'tests/OpaqueRectTrackingContentLayerDelegateTest.cpp',
       'tests/OpenTypeVerticalDataTest.cpp',
       'tests/PageSerializerTest.cpp',
       'tests/PaintAggregatorTest.cpp',
       'tests/PopupContainerTest.cpp',
       'tests/PrerenderingTest.cpp',
       'tests/ProgrammaticScrollTest.cpp',
-      'tests/RegionTest.cpp',
       'tests/RenderTableCellTest.cpp',
       'tests/RenderTableRowTest.cpp',
       'tests/ScrollingCoordinatorChromiumTest.cpp',
       'tests/URLTestHelpers.cpp',
       'tests/URLTestHelpers.h',
       'tests/WebFrameTest.cpp',
       'tests/WebImageTest.cpp',
       'tests/WebInputEventConversionTest.cpp',
       'tests/WebInputEventFactoryTestMac.mm',
       'tests/WebPageNewSerializerTest.cpp',
@@ skipping 45 matching lines @@
         {
           'web_unittest_files': [
             'tests/KeyCodeConversionTestGtk.cpp',
             'tests/WebInputEventFactoryTestGtk.cpp',
           ],
         }
       ],
     ],
   },
 }