Revert the latest set of platform changes.

src/platform-win32.cc

Index: src/platform-win32.cc
diff --git a/src/platform-win32.cc b/src/platform-win32.cc
index c0f049c52d9bacbee9f286c02b0c00f9df609b64..292c24a3dace86c6500acbd6634536d0dea7ddb6 100644
--- a/src/platform-win32.cc
+++ b/src/platform-win32.cc
@@ -1705,6 +1705,46 @@ void Thread::YieldCPU() {
 
 
 // ----------------------------------------------------------------------------
+// Win32 mutex support.
+//
+// On Win32 mutexes are implemented using CRITICAL_SECTION objects. These are
+// faster than Win32 Mutex objects because they are implemented using user mode
+// atomic instructions. Therefore we only do ring transitions if there is lock
+// contention.
+
+class Win32Mutex : public Mutex {
+ public:
+  Win32Mutex() { InitializeCriticalSection(&cs_); }
+
+  virtual ~Win32Mutex() { DeleteCriticalSection(&cs_); }
+
+  virtual int Lock() {
+    EnterCriticalSection(&cs_);
+    return 0;
+  }
+
+  virtual int Unlock() {
+    LeaveCriticalSection(&cs_);
+    return 0;
+  }
+
+
+  virtual bool TryLock() {
+    // Returns non-zero if critical section is entered successfully entered.
+    return TryEnterCriticalSection(&cs_);
+  }
+
+ private:
+  CRITICAL_SECTION cs_;  // Critical section used for mutex
+};
+
+
+Mutex* OS::CreateMutex() {
+  return new Win32Mutex();
+}
+
+
+// ----------------------------------------------------------------------------
 // Win32 semaphore support.
 //
 // On Win32 semaphores are implemented using Win32 Semaphore objects. The
@@ -1947,7 +1987,7 @@ void OS::SetUp() {
   // call this setup code within the same millisecond.
   uint64_t seed = static_cast<uint64_t>(TimeCurrentMillis());
   srand(static_cast<unsigned int>(seed));
-  limit_mutex = new Mutex;
+  limit_mutex = CreateMutex();
 }