Turn ViewportAnchors into stack allocated objects.

Source/web/web.gypi

 {
   'variables': {
     'web_files': [
       'AssertMatchingEnums.cpp',
       'AssociatedURLLoader.cpp',
       'AssociatedURLLoader.h',
       'ChromeClientImpl.cpp',
       'ChromeClientImpl.h',
       'ColorChooserPopupUIController.cpp',
       'ColorChooserPopupUIController.h',
@@ skipping 98 matching lines @@
       'StorageQuotaClientImpl.cpp',
       'StorageQuotaClientImpl.h',
       'SuspendableScriptExecutor.cpp',
       'SuspendableScriptExecutor.h',
       'TextFinder.cpp',
       'TextFinder.h',
       'UserMediaClientImpl.cpp',
       'UserMediaClientImpl.h',
       'ValidationMessageClientImpl.cpp',
       'ValidationMessageClientImpl.h',
-      'ViewportAnchor.cpp',
       'ViewportAnchor.h',
       'WebAXObject.cpp',
       'WebArrayBuffer.cpp',
       'WebArrayBufferConverter.cpp',
       'WebArrayBufferView.cpp',
       'WebBindings.cpp',
       'WebBlob.cpp',
       'WebCache.cpp',
       'WebCachedURLRequest.cpp',
       'WebColorName.cpp',
@@ skipping 226 matching lines @@
       ['os_posix==1 and OS!="mac"',
         {
           'web_unittest_files': [
             'tests/LocaleICUTest.cpp',
           ],
         }
       ],
     ],
   },
 }