Oilpan: have xml/ objects on the heap by default.

Source/core/core.gypi

 {
     'includes': [
         'core_generated.gypi',
     ],
     'variables': {
         # Files for which bindings (.cpp and .h files) will be generated
         'core_idl_files': [
             'animation/Animation.idl',
             'animation/AnimationEffect.idl',
             'animation/AnimationNode.idl',
@@ skipping 2040 matching lines @@
             'xml/XMLSerializer.cpp',
             'xml/XMLSerializer.h',
             'xml/XPathEvaluator.cpp',
             'xml/XPathEvaluator.h',
             'xml/XPathExpression.cpp',
             'xml/XPathExpression.h',
             'xml/XPathExpressionNode.cpp',
             'xml/XPathExpressionNode.h',
             'xml/XPathFunctions.cpp',
             'xml/XPathFunctions.h',
-            'xml/XPathNSResolver.cpp',
             'xml/XPathNSResolver.h',
             'xml/XPathNodeSet.cpp',
             'xml/XPathNodeSet.h',
             'xml/XPathParser.cpp',
             'xml/XPathParser.h',
             'xml/XPathPath.cpp',
             'xml/XPathPath.h',
             'xml/XPathPredicate.cpp',
             'xml/XPathPredicate.h',
             'xml/XPathResult.cpp',
@@ skipping 1792 matching lines @@
             'paint/LayerClipRecorderTest.cpp',
             'paint/LayoutObjectDrawingRecorderTest.cpp',
             'paint/TextPainterTest.cpp',
             'streams/ReadableStreamReaderTest.cpp',
             'streams/ReadableStreamTest.cpp',
             'testing/PrivateScriptTestTest.cpp',
             'xml/parser/SharedBufferReaderTest.cpp',
         ],
     }
 }