Replace OS::NumberOfCores() with CPU::NumberOfProcessorsOnline().

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 30 matching lines @@
   CHECK(!cpu.has_sse() || cpu.has_mmx());
   CHECK(!cpu.has_sse2() || cpu.has_sse());
   CHECK(!cpu.has_sse3() || cpu.has_sse2());
   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);
+}