Some inline ARM assembly for saturated arithmetic, a small speed-up for

Source/wtf/wtf.gypi

 # For GN compatibility, this file can not have any conditions.
 {
     'variables': {
         'wtf_files': [
             'ASCIICType.h',
             'Alignment.h',
             'ArrayBuffer.cpp',
             'ArrayBuffer.h',
             'ArrayBufferBuilder.cpp',
             'ArrayBufferBuilder.h',
@@ skipping 117 matching lines @@
             'Uint32Array.h',
             'Uint8Array.h',
             'Vector.h',
             'VectorTraits.h',
             'WTF.cpp',
             'WTF.h',
             'WTFExport.h',
             'WTFThreadData.cpp',
             'WTFThreadData.h',
             'WeakPtr.h',
+            'asm/SaturatedArithmeticARM.h',
             'dtoa.cpp',
             'dtoa.h',
             'dtoa/bignum-dtoa.cc',
             'dtoa/bignum-dtoa.h',
             'dtoa/bignum.cc',
             'dtoa/bignum.h',
             'dtoa/cached-powers.cc',
             'dtoa/cached-powers.h',
             'dtoa/diy-fp.cc',
             'dtoa/diy-fp.h',
@@ skipping 82 matching lines @@
             'text/TextCodecUTF8Test.cpp',
             'text/WTFStringTest.cpp',
         ],
         'wtf_unittest_helper_files': [
             'testing/WTFTestHelpers.cpp',
             'testing/WTFTestHelpers.h',
             'testing/WTFUnitTestHelpersExport.h',
         ],
     },
 }