Initial commit of sync engine code to browser/sync....

chrome/browser/sync/util/highres_timer-win32.cc

+// Copyright (c) 2009 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.
+//
+// High resolution timer functions for use in Windows.
+
+#include "chrome/browser/sync/util/highres_timer.h"
+
+bool HighresTimer::perf_freq_collected_ = false;
+ULONGLONG HighresTimer::perf_freq_ = 0;
+
+ULONGLONG HighresTimer::GetElapsedMs() const {
+  ULONGLONG end_time = GetCurrentTicks();
+
+  // Scale to ms and round to nearest ms - rounding is important because
+  // otherwise the truncation error may accumulate e.g. in sums.
+  //
+  // Given infinite resolution, this expression could be written as:
+  //  trunc((end - start (units:freq*sec))/freq (units:sec) *
+  //                1000 (unit:ms) + 1/2 (unit:ms))
+  ULONGLONG freq = GetTimerFrequency();
+  return ((end_time - start_ticks_) * 1000L + freq / 2) / freq;
+}
+
+ULONGLONG HighresTimer::GetElapsedSec() const {
+  ULONGLONG end_time = GetCurrentTicks();
+
+  // Round to nearest ms - rounding is important because otherwise the
+  // truncation error may accumulate e.g. in sums.
+  //
+  // Given infinite resolution, this expression could be written as:
+  //  trunc((end - start (units:freq*sec))/freq (unit:sec) + 1/2 (unit:sec))
+  ULONGLONG freq = GetTimerFrequency();
+  return ((end_time - start_ticks_) + freq / 2) / freq;
+}
+
+void HighresTimer::CollectPerfFreq() {
+  LARGE_INTEGER freq;
+
+  // Note that this is racy. It's OK, however, because even concurrent
+  // executions of this are idempotent.
+  if (::QueryPerformanceFrequency(&freq)) {
+    perf_freq_ = freq.QuadPart;
+    perf_freq_collected_ = true;
+  }
+}