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

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index f52bb43d9c0ca8696c49cf4b8efe886fdba618b5..c136631f00272659ed76f845ca8fd59c965ddd4d 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -991,13 +991,6 @@ void OS::Sleep(int milliseconds) {
 }
 
 
-int OS::NumberOfCores() {
-  SYSTEM_INFO info;
-  GetSystemInfo(&info);
-  return info.dwNumberOfProcessors;
-}
-
-
 void OS::Abort() {
   if (IsDebuggerPresent() || FLAG_break_on_abort) {
     DebugBreak();