WIP (Introduce WTF::NonNullPtr<T>.)

Source/wtf/wtf.gypi

 {
     'variables': {
         'wtf_files': [
             'ASCIICType.h',
             'Alignment.h',
             'ArrayBuffer.cpp',
             'ArrayBuffer.h',
             'ArrayBufferContents.cpp',
             'ArrayBufferContents.h',
             'ArrayBufferDeallocationObserver.h',
@@ skipping 56 matching lines @@
             'LeakAnnotations.h',
             'LinkedStack.h',
             'ListHashSet.h',
             'Locker.h',
             'MainThread.cpp',
             'MainThread.h',
             'MallocZoneSupport.h',
             'MathExtras.h',
             'MessageQueue.h',
             'NonCopyingSort.h',
+            'NonNullPtr.h',
             'Noncopyable.h',
             'NotFound.h',
             'NullPtr.cpp',
             'NullPtr.h',
             'NumberOfCores.cpp',
             'NumberOfCores.h',
             'OwnArrayPtr.h',
             'OwnPtr.h',
             'OwnPtrCommon.h',
             'PageAllocator.cpp',
@@ skipping 146 matching lines @@
             'tests/StringImpl.cpp',
             'tests/StringOperators.cpp',
             'tests/TemporaryChange.cpp',
             'tests/Vector.cpp',
             'tests/VectorBasic.cpp',
             'tests/VectorReverse.cpp',
             'tests/WTFString.cpp',
         ],
     },
 }