Merges the two different page serializers

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'ApplicationCacheHost.cpp',
       'ApplicationCacheHostInternal.h',
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'AutofillPopupMenuClient.cpp',
       'AutofillPopupMenuClient.h',
@@ skipping 177 matching lines @@
       'WebMediaStreamRegistry.cpp',
       'WebNetworkStateNotifier.cpp',
       'WebNode.cpp',
       'WebNodeCollection.cpp',
       'WebNodeList.cpp',
       'WebNotification.cpp',
       'WebOptionElement.cpp',
       'WebPagePopupImpl.cpp',
       'WebPagePopupImpl.h',
       'WebPageSerializer.cpp',
-      'WebPageSerializerImpl.cpp',
-      'WebPageSerializerImpl.h',
       'WebPasswordFormData.cpp',
       'WebPasswordFormUtils.cpp',
       'WebPasswordFormUtils.h',
       'WebPerformance.cpp',
       'WebPluginContainerImpl.cpp',
       'WebPluginContainerImpl.h',
       'WebPluginDocument.cpp',
       'WebPluginLoadObserver.cpp',
       'WebPluginLoadObserver.h',
       'WebPluginScrollbarImpl.cpp',
@@ skipping 76 matching lines @@
       'tests/GIFImageDecoderTest.cpp',
       'tests/GraphicsContextTest.cpp',
       'tests/GraphicsLayerTest.cpp',
       'tests/ImageFilterBuilderTest.cpp',
       'tests/ImageLayerChromiumTest.cpp',
       'tests/JPEGImageDecoderTest.cpp',
       'tests/KeyboardTest.cpp',
       'tests/LinkHighlightTest.cpp',
       'tests/ListenerLeakTest.cpp',
       'tests/MemoryInfo.cpp',
+      'tests/MHTMLTest.cpp',
       'tests/MockWebGraphicsContext3D.h',
       'tests/OpaqueRectTrackingContentLayerDelegateTest.cpp',
       'tests/OpenTypeVerticalDataTest.cpp',
       'tests/PageSerializerTest.cpp',
       'tests/PaintAggregatorTest.cpp',
       'tests/PopupContainerTest.cpp',
       'tests/PrerenderingTest.cpp',
       'tests/ProgrammaticScrollTest.cpp',
       'tests/RenderTableCellTest.cpp',
       'tests/RenderTableRowTest.cpp',
       'tests/ScrollingCoordinatorChromiumTest.cpp',
       'tests/SpinLockTest.cpp',
       'tests/TouchActionTest.cpp',
       'tests/URLTestHelpers.cpp',
       'tests/URLTestHelpers.h',
       'tests/ViewportTest.cpp',
       'tests/WebFrameTest.cpp',
       'tests/WebImageTest.cpp',
       'tests/WebInputEventConversionTest.cpp',
       'tests/WebInputEventFactoryTestMac.mm',
       'tests/WEBPImageDecoderTest.cpp',
-      'tests/WebPageNewSerializerTest.cpp',
-      'tests/WebPageSerializerTest.cpp',
       'tests/WebPluginContainerTest.cpp',
       'tests/WebSearchableFormDataTest.cpp',
       'tests/WebSelectorTest.cpp',
       'tests/WebURLRequestTest.cpp',
       'tests/WebURLResponseTest.cpp',
       'tests/WebUserGestureTokenTest.cpp',
       'tests/WebViewTest.cpp',
     ],
     'conditions': [
       ['OS=="win"',
         {
           'web_unittest_files': [
             'tests/LocaleWinTest.cpp',
             # FIXME: Port PopupMenuTest to Linux and Mac.
             'tests/PopupMenuTest.cpp',
             'tests/TransparencyWinTest.cpp',
-            'tests/WebPageNewSerializerTest.cpp',
-            'tests/WebPageSerializerTest.cpp',
           ],
         }
       ],
       ['OS=="win" and "ENABLE_HARFBUZZ_ON_WINDOWS=0" in feature_defines',
         {
           'web_unittest_files': [
             'tests/UniscribeHelperTest.cpp',
           ]
         }
       ],
@@ skipping 23 matching lines @@
         {
           'web_unittest_files': [
             'tests/KeyCodeConversionTestGtk.cpp',
             'tests/WebInputEventFactoryTestGtk.cpp',
           ],
         }
       ],
     ],
   },
 }