Defer style recalc when inserting extension stylesheets.

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'BackForwardClientImpl.cpp',
       'BackForwardClientImpl.h',
       'ChromeClientImpl.cpp',
       'ChromeClientImpl.h',
@@ skipping 274 matching lines @@
       'tests/ProgrammaticScrollTest.cpp',
       'tests/RenderTableCellTest.cpp',
       'tests/RenderTableRowTest.cpp',
       'tests/ScrollingCoordinatorChromiumTest.cpp',
       'tests/SpinLockTest.cpp',
       'tests/TextFinderTest.cpp',
       'tests/TouchActionTest.cpp',
       'tests/URLTestHelpers.cpp',
       'tests/URLTestHelpers.h',
       'tests/ViewportTest.cpp',
+      'tests/WebDocumentTest.cpp',
       'tests/WebFrameTest.cpp',
       'tests/WebHelperPluginTest.cpp',
       'tests/WebImageTest.cpp',
       'tests/WebInputEventConversionTest.cpp',
       'tests/WebInputEventFactoryTestMac.mm',
       'tests/WebPageNewSerializerTest.cpp',
       'tests/WebPageSerializerTest.cpp',
       'tests/WebPluginContainerTest.cpp',
       'tests/WebScopedWindowFocusAllowedIndicatorTest.cpp',
       'tests/WebSearchableFormDataTest.cpp',
@@ skipping 31 matching lines @@
       ['os_posix==1 and OS!="mac"',
         {
           'web_unittest_files': [
             'tests/LocaleICUTest.cpp',
           ],
         }
       ],
     ],
   },
 }