Revert "[PartitionAlloc] Implement SpinningMutex on macOS."

This reverts commit a777fd4b.

Reason for revert: Suspect for crbug.com/1151948

Original change's description:
> [PartitionAlloc] Implement SpinningMutex on macOS.
>
> macOS has futex()-like locks in pthread, meaning that SpinningFutex can
> be useful there, the same way it is on Windows. Use pthread to implement
> it.
>
> Bug: 998048
> Change-Id: I77df835baf2f099eedcfcee675f7a56ed6b3bb2b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2550797
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Commit-Queue: Benoit L <lizeb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#830175}

TBR=haraken@chromium.org,lizeb@chromium.org

Change-Id: I636660d7834a80595578ee18ad80b7dfe42d6ed6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 998048, 1151948
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2555177Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830206}

base/allocator/partition_allocator/spinning_mutex.cc

@@ -70,19 +70,12 @@ void SpinningMutex::LockSlow() {
   }
 }
 
-#elif defined(OS_WIN)
+#else
 
 void SpinningMutex::LockSlow() {
   ::AcquireSRWLockExclusive(reinterpret_cast<PSRWLOCK>(&lock_));
 }
 
-#elif defined(OS_APPLE)
-
-void SpinningMutex::LockSlow() {
-  int retval = pthread_mutex_lock(&lock_);
-  PA_DCHECK(retval == 0);
-}
-
 #endif
 }  // namespace internal
 }  // namespace base

base/allocator/partition_allocator/spinning_mutex.h

@@ -8,7 +8,6 @@
 #include <algorithm>
 #include <atomic>
 
-#include "base/allocator/partition_allocator/partition_alloc_check.h"
 #include "base/allocator/partition_allocator/yield_processor.h"
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
@@ -19,20 +18,11 @@
 #include <windows.h>
 #endif
 
-#if defined(OS_APPLE)
-#include <errno.h>
-#include <pthread.h>
-#endif
-
 #if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(OS_ANDROID)
 #define PA_HAS_LINUX_KERNEL
 #endif
 
-// Linux:   futex() makes Try() fast without a syscall.
-// Windows: SRWLock are futex()-like.
-// Apple:   pthread has futex()-like locks (see pthread_mutex.c in Apple's
-//          libpthread).
-#if defined(PA_HAS_LINUX_KERNEL) || defined(OS_WIN) || defined(OS_APPLE)
+#if defined(PA_HAS_LINUX_KERNEL) || defined(OS_WIN)
 #define PA_HAS_SPINNING_MUTEX
 #endif
 
@@ -85,10 +75,8 @@ class LOCKABLE BASE_EXPORT SpinningMutex {
   static constexpr int kLockedContended = 2;
 
   std::atomic<int32_t> state_{kUnlocked};
-#elif defined(OS_WIN)
+#else
   SRWLOCK lock_ = SRWLOCK_INIT;
-#elif defined(OS_APPLE)
-  pthread_mutex_t lock_ = PTHREAD_MUTEX_INITIALIZER;
 #endif
 };
 
@@ -153,7 +141,7 @@ ALWAYS_INLINE void SpinningMutex::Release() {
   }
 }
 
-#elif defined(OS_WIN)
+#else
 
 ALWAYS_INLINE bool SpinningMutex::Try() {
   return !!::TryAcquireSRWLockExclusive(reinterpret_cast<PSRWLOCK>(&lock_));
@@ -163,19 +151,6 @@ ALWAYS_INLINE void SpinningMutex::Release() {
   ::ReleaseSRWLockExclusive(reinterpret_cast<PSRWLOCK>(&lock_));
 }
 
-#elif defined(OS_APPLE)
-
-ALWAYS_INLINE bool SpinningMutex::Try() {
-  int retval = pthread_mutex_trylock(&lock_);
-  PA_DCHECK(retval == 0 || retval == EBUSY);
-  return retval == 0;
-}
-
-ALWAYS_INLINE void SpinningMutex::Release() {
-  int retval = pthread_mutex_unlock(&lock_);
-  PA_DCHECK(retval == 0);
-}
-
 #endif
 
 }  // namespace internal