[sensors] [mac] Implement ambient light sensor for macOS

content/common/one_writer_seqlock.cc

Index: content/common/one_writer_seqlock.cc
diff --git a/content/common/one_writer_seqlock.cc b/content/common/one_writer_seqlock.cc
deleted file mode 100644
index fa0c8b2d0cf424a5cfa09ca18a1b5749259de8f8..0000000000000000000000000000000000000000
--- a/content/common/one_writer_seqlock.cc
+++ /dev/null
@@ -1,49 +0,0 @@
-// Copyright 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "content/common/one_writer_seqlock.h"
-
-namespace content {
-
-OneWriterSeqLock::OneWriterSeqLock()
-  : sequence_(0) {
-}
-
-base::subtle::Atomic32 OneWriterSeqLock::ReadBegin() {
-  base::subtle::Atomic32 version;
-  for (;;) {
-    version = base::subtle::NoBarrier_Load(&sequence_);
-
-    // If the counter is even, then the associated data might be in a
-    // consistent state, so we can try to read.
-    if ((version & 1) == 0)
-      break;
-
-    // Otherwise, the writer is in the middle of an update. Retry the read.
-    base::PlatformThread::YieldCurrentThread();
-  }
-  return version;
-}
-
-bool OneWriterSeqLock::ReadRetry(base::subtle::Atomic32 version) {
-  // If the sequence number was updated then a read should be re-attempted.
-  // -- Load fence, read membarrier
-  return base::subtle::Release_Load(&sequence_) != version;
-}
-
-void OneWriterSeqLock::WriteBegin() {
-  // Increment the sequence number to odd to indicate the beginning of a write
-  // update.
-  base::subtle::Barrier_AtomicIncrement(&sequence_, 1);
-  // -- Store fence, write membarrier
-}
-
-void OneWriterSeqLock::WriteEnd() {
-  // Increment the sequence to an even number to indicate the completion of
-  // a write update.
-  // -- Store fence, write membarrier
-  base::subtle::Barrier_AtomicIncrement(&sequence_, 1);
-}
-
-} // namespace content