Never cast Attr to ContainerNode based on nodeType ATTRIBUTE_NODE

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 3817 matching lines @@
             'css/invalidation/DescendantInvalidationSetTest.cpp',
             'css/parser/CSSParserValuesTest.cpp',
             'css/parser/CSSPropertyParserTest.cpp',
             'css/parser/CSSSelectorParserTest.cpp',
             'css/parser/CSSTokenizerTest.cpp',
             'css/parser/MediaConditionTest.cpp',
             'css/parser/SizesAttributeParserTest.cpp',
             'css/parser/SizesCalcParserTest.cpp',
             'css/resolver/FontBuilderTest.cpp',
             'dom/ActiveDOMObjectTest.cpp',
+            'dom/AttrTest.cpp',
             'dom/CrossThreadTaskTest.cpp',
             'dom/DOMImplementationTest.cpp',
             'dom/DocumentMarkerControllerTest.cpp',
             'dom/DocumentTest.cpp',
             'dom/MainThreadTaskRunnerTest.cpp',
             'dom/NthIndexCacheTest.cpp',
             'dom/RangeTest.cpp',
             'dom/ScriptRunnerTest.cpp',
             'dom/TreeScopeStyleSheetCollectionTest.cpp',
             'dom/TreeScopeTest.cpp',
@@ skipping 73 matching lines @@
             'style/ComputedStyleTest.cpp',
             'style/OutlineValueTest.cpp',
             'style/SVGComputedStyleTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'timing/MemoryInfoTest.cpp',
             'workers/WorkerThreadTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }