Merge WTF::initializeMainThread into WTF::initialize

third_party/WebKit/Source/wtf/wtf.gypi

 # For GN compatibility, this file can not have any conditions.
 {
     'variables': {
         'wtf_files': [
             'ASCIICType.cpp',
             'ASCIICType.h',
             'AddressSanitizer.h',
             'AddressSpaceRandomization.cpp',
             'AddressSpaceRandomization.h',
             'Alignment.h',
@@ skipping 55 matching lines @@
             'InstanceCounter.cpp',
             'InstanceCounter.h',
             'Int16Array.h',
             'Int32Array.h',
             'Int8Array.h',
             'IntegralTypedArrayBase.h',
             'LeakAnnotations.h',
             'LinkedStack.h',
             'ListHashSet.h',
             'Locker.h',
-            'MainThread.cpp',
-            'MainThread.h',
             'MathExtras.h',
             'NonCopyingSort.h',
             'Noncopyable.h',
             'NotFound.h',
             'Optional.h',
             'OwnPtr.h',
             'OwnPtrCommon.h',
             'PageAllocator.cpp',
             'PageAllocator.h',
             'PartitionAlloc.cpp',
@@ skipping 139 matching lines @@
             'text/StringBufferTest.cpp',
             'text/StringBuilderTest.cpp',
             'text/StringImplTest.cpp',
             'text/StringOperatorsTest.cpp',
             'text/TextCodecReplacementTest.cpp',
             'text/TextCodecUTF8Test.cpp',
             'text/WTFStringTest.cpp',
         ],
     },
 }