Add 8bit Content-Transfer-Encoding support for reading MHTML files

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'ApplicationCacheHost.cpp',
       'ApplicationCacheHostInternal.h',
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'AsyncFileSystemChromium.cpp',
       'AsyncFileSystemChromium.h',
@@ skipping 290 matching lines @@
       'tests/FilterOperationsTest.cpp',
       'tests/FrameLoaderClientImplTest.cpp',
       'tests/FrameTestHelpers.cpp',
       'tests/FrameTestHelpers.h',
       'tests/GraphicsLayerTest.cpp',
       'tests/ImageFilterBuilderTest.cpp',
       'tests/ImageLayerChromiumTest.cpp',
       'tests/KeyboardTest.cpp',
       'tests/LinkHighlightTest.cpp',
       'tests/ListenerLeakTest.cpp',
+      'tests/MHTMLTest.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/RenderLayerBackingTest.cpp',
@@ skipping 54 matching lines @@
         {
           'web_unittest_files': [
             'tests/KeyCodeConversionTestGtk.cpp',
             'tests/WebInputEventFactoryTestGtk.cpp',
           ],
         }
       ],
     ],
   },
 }