Move PseudoElements storage to their own object.

third_party/WebKit/Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/KeyframeEffect.idl',
             'animation/EffectModel.idl',
             'animation/AnimationEffectReadOnly.idl',
@@ skipping 2549 matching lines @@
             'dom/NthIndexCache.h',
             'dom/ParentNode.h',
             'dom/PendingScript.cpp',
             'dom/PresentationAttributeStyle.cpp',
             'dom/PresentationAttributeStyle.h',
             'dom/ProcessingInstruction.cpp',
             'dom/ProcessingInstruction.h',
             'dom/CompositorProxiedPropertySet.cpp',
             'dom/CompositorProxiedPropertySet.h',
             'dom/PseudoElement.cpp',
+            'dom/PseudoElementData.h',
             'dom/QualifiedName.cpp',
             'dom/Range.cpp',
             'dom/RawDataDocumentParser.h',
             'dom/RemoteSecurityContext.cpp',
             'dom/RemoteSecurityContext.h',
             'dom/SandboxFlags.cpp',
             'dom/SandboxFlags.h',
             'dom/ScopedWindowFocusAllowedIndicator.h',
             'dom/ScriptLoader.cpp',
             'dom/ScriptLoader.h',
@@ skipping 1540 matching lines @@
             'svg/SVGPathParserTest.cpp',
             'svg/UnsafeSVGAttributeSanitizationTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'workers/WorkerThreadTestHelper.h',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }