Add interface to system trace clock.

base/time_posix.cc

 // Copyright (c) 2012 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 "base/time.h"
 
 #include <sys/time.h>
 #include <time.h>
 #include <unistd.h>
 
@@ skipping 210 matching lines @@
 
 #else  // _POSIX_MONOTONIC_CLOCK
 #error No usable tick clock function on this platform.
 #endif  // _POSIX_MONOTONIC_CLOCK
 
 // static
 TimeTicks TimeTicks::HighResNow() {
   return Now();
 }
 
+#if defined(OS_POSIX) && defined(CLOCK_SYSTEM_TRACE)
+
+// static
+TimeTicks TimeTicks::NowFromSystemTraceTime() {
+  uint64_t absolute_micro;
+
+  struct timespec ts;
+  if (clock_gettime(CLOCK_SYSTEM_TRACE, &ts) != 0) {
+    NOTREACHED() << "clock_gettime(CLOCK_SYSTEM_TRACE) failed.";
+    return HighResNow();
+  }
+
+  absolute_micro =
+      (static_cast<int64>(ts.tv_sec) * Time::kMicrosecondsPerSecond) +
+      (static_cast<int64>(ts.tv_nsec) / Time::kNanosecondsPerMicrosecond);
+
+  return TimeTicks(absolute_micro);
+}
+
+#else // !(defined(OS_POSIX) && defined(CLOCK_SYSTEM_TRACE))
+
+// static
+TimeTicks TimeTicks::NowFromSystemTraceTime() {
+  return HighResNow();
+}
+
+#endif // defined(OS_POSIX) && defined(CLOCK_SYSTEM_TRACE)
+
 #endif  // !OS_MACOSX
 
 struct timeval Time::ToTimeVal() const {
   struct timeval result;
   int64 us = us_ - kTimeTToMicrosecondsOffset;
   result.tv_sec = us / Time::kMicrosecondsPerSecond;
   result.tv_usec = us % Time::kMicrosecondsPerSecond;
   return result;
 }
 
 }  // namespace base