Revert 153294 "Remove AtomicStringImpl."

trunk/Source/wtf/wtf.gypi

 {
     'variables': {
         'wtf_files': [
             'ASCIICType.h',
             'Alignment.h',
             'ArrayBuffer.cpp',
             'ArrayBuffer.h',
             'ArrayBufferContents.cpp',
             'ArrayBufferContents.h',
             'ArrayBufferDeallocationObserver.h',
@@ skipping 167 matching lines @@
             'dtoa/fast-dtoa.h',
             'dtoa/fixed-dtoa.cc',
             'dtoa/fixed-dtoa.h',
             'dtoa/strtod.cc',
             'dtoa/strtod.h',
             'dtoa/utils.h',
             'text/ASCIIFastPath.h',
             'text/AtomicString.cpp',
             'text/AtomicString.h',
             'text/AtomicStringHash.h',
+            'text/AtomicStringImpl.h',
             'text/Base64.cpp',
             'text/Base64.h',
             'text/CString.cpp',
             'text/CString.h',
             'text/IntegerToStringConversion.h',
             'text/StringBuffer.h',
             'text/StringBuilder.cpp',
             'text/StringBuilder.h',
             'text/StringConcatenate.h',
             'text/StringHash.h',
@@ skipping 43 matching lines @@
             'tests/StringImpl.cpp',
             'tests/StringOperators.cpp',
             'tests/TemporaryChange.cpp',
             'tests/Vector.cpp',
             'tests/VectorBasic.cpp',
             'tests/VectorReverse.cpp',
             'tests/WTFString.cpp',
         ],
     },
 }