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

base/time/time_mac.cc

Index: base/time/time_mac.cc
diff --git a/base/time/time_mac.cc b/base/time/time_mac.cc
index f0c780449b7b23ae89fbd1cad7d86b3905f88a18..b7bac35bb637168a25cee9cad872165dc08913f1 100644
--- a/base/time/time_mac.cc
+++ b/base/time/time_mac.cc
@@ -237,6 +237,15 @@ bool TimeTicks::IsHighResolution() {
 }
 
 // static
+TimeTicks::Clock TimeTicks::GetClock() {
+#if defined(OS_IOS)
+  return Clock::IOS_CF_ABSOLUTE_TIME_MINUS_KERN_BOOTTIME;
+#else
+  return Clock::MAC_MACH_ABSOLUTE_TIME;
+#endif  // defined(OS_IOS)
+}
+
+// static
 ThreadTicks ThreadTicks::Now() {
   return ThreadTicks(ComputeThreadTicks());
 }