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

base/time/time_posix.cc

Index: base/time/time_posix.cc
diff --git a/base/time/time_posix.cc b/base/time/time_posix.cc
index 4aadee618a0fb3a452edf945ab4b7e9fc3ac8a14..22e304320f8ae4510a56bb05d27cc8b232c220f9 100644
--- a/base/time/time_posix.cc
+++ b/base/time/time_posix.cc
@@ -93,6 +93,9 @@ int64_t ConvertTimespecToMicros(const struct timespec& ts) {
 #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) {
@@ -312,6 +315,11 @@ TimeTicks TimeTicks::Now() {
 }
 
 // static
+std::string TimeTicks::ClockId() {
+  return kLinuxMonotonicClockId;
+}
+
+// static
 bool TimeTicks::IsHighResolution() {
   return true;
 }