time: Add a static TimeTicks method that returns the underlying clock

base/time/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/time.h"
 
 #include <stdint.h>
 #include <sys/time.h>
 #include <time.h>
 #if defined(OS_ANDROID) && !defined(__LP64__)
@@ skipping 75 matching lines @@
   return result.ValueOrDie();
 }
 
 // Helper function to get results from clock_gettime() and convert to a
 // microsecond timebase. Minimum requirement is MONOTONIC_CLOCK to be supported
 // on the system. FreeBSD 6 has CLOCK_MONOTONIC but defines
 // _POSIX_MONOTONIC_CLOCK to -1.
 #if (defined(OS_POSIX) &&                                               \
      defined(_POSIX_MONOTONIC_CLOCK) && _POSIX_MONOTONIC_CLOCK >= 0) || \
     defined(OS_BSD) || defined(OS_ANDROID)
+
+const char* kLinuxMonotonicClockId = "LINUX_CLOCK_MONOTONIC_MICROS";
+
 int64_t ClockNow(clockid_t clk_id) {
   struct timespec ts;
   if (clock_gettime(clk_id, &ts) != 0) {
     NOTREACHED() << "clock_gettime(" << clk_id << ") failed.";
     return 0;
   }
   return ConvertTimespecToMicros(ts);
 }
 #else  // _POSIX_MONOTONIC_CLOCK
 #error No usable tick clock function on this platform.
@@ skipping 199 matching lines @@
       kWindowsEpochDeltaMicroseconds);
 }
 
 // TimeTicks ------------------------------------------------------------------
 // static
 TimeTicks TimeTicks::Now() {
   return TimeTicks(ClockNow(CLOCK_MONOTONIC));
 }
 
 // static
+std::string TimeTicks::ClockId() {
+  return kLinuxMonotonicClockId;
+}
+
+// static
 bool TimeTicks::IsHighResolution() {
   return true;
 }
 
 // static
 ThreadTicks ThreadTicks::Now() {
 #if (defined(_POSIX_THREAD_CPUTIME) && (_POSIX_THREAD_CPUTIME >= 0)) || \
     defined(OS_ANDROID)
   return ThreadTicks(ClockNow(CLOCK_THREAD_CPUTIME_ID));
 #else
@@ skipping 29 matching lines @@
     result.tv_usec = static_cast<suseconds_t>(Time::kMicrosecondsPerSecond) - 1;
     return result;
   }
   int64_t us = us_ - kTimeTToMicrosecondsOffset;
   result.tv_sec = us / Time::kMicrosecondsPerSecond;
   result.tv_usec = us % Time::kMicrosecondsPerSecond;
   return result;
 }
 
 }  // namespace base