Move NumberOfProcessorsOnline from CPU to OS

test/cctest/test-cpu.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 33 matching lines @@
   CHECK(!cpu.has_ssse3() || cpu.has_sse3());
   CHECK(!cpu.has_sse41() || cpu.has_sse3());
   CHECK(!cpu.has_sse42() || cpu.has_sse41());
 
   // arm features
   CHECK(!cpu.has_vfp3_d32() || cpu.has_vfp3());
 }
 
 
 TEST(NumberOfProcessorsOnline) {
-  CHECK_GT(CPU::NumberOfProcessorsOnline(), 0);
+  CHECK_GT(OS::NumberOfProcessorsOnline(), 0);
 }