Revert "Remove old serializer" It caused a regression, crbug.com/510422

Source/web/web.gypi

Index: Source/web/web.gypi
diff --git a/Source/web/web.gypi b/Source/web/web.gypi
index 6c97160002ade4b11761a5d437006c05fa3a8fc7..68f18a113a0d80b091f9a3940bf043842ba17b0e 100644
--- a/Source/web/web.gypi
+++ b/Source/web/web.gypi
@@ -191,6 +191,8 @@
       'WebPagePopupImpl.cpp',
       'WebPagePopupImpl.h',
       'WebPageSerializer.cpp',
+      'WebPageSerializerImpl.cpp',
+      'WebPageSerializerImpl.h',
       'WebPerformance.cpp',
       'WebPluginContainerImpl.cpp',
       'WebPluginContainerImpl.h',
@@ -299,6 +301,7 @@
       'tests/WebImageTest.cpp',
       'tests/WebInputEventConversionTest.cpp',
       'tests/WebInputEventFactoryTestMac.mm',
+      'tests/WebPageSerializerTest.cpp',
       'tests/WebPluginContainerTest.cpp',
       'tests/WebScopedWindowFocusAllowedIndicatorTest.cpp',
       'tests/WebSearchableFormDataTest.cpp',
@@ -310,6 +313,13 @@
       'tests/WebViewTest.cpp',
     ],
     'conditions': [
+      ['OS=="win"',
+        {
+          'web_unittest_files': [
+            'tests/WebPageSerializerTest.cpp',
+          ],
+        }
+      ],
       ['OS!="mac"',
         {
           'web_unittest_files': [