Add UMA for High Resolution Timer Usage

base/time/time.h

Index: base/time/time.h
diff --git a/base/time/time.h b/base/time/time.h
index 3ff215cbbc4132690bc11b41fe2aaec6b7306989..92430427b9c6e490e8b8905bde79553badb173a7 100644
--- a/base/time/time.h
+++ b/base/time/time.h
@@ -549,6 +549,15 @@ class BASE_EXPORT Time : public time_internal::TimeBase<Time> {
   // This is provided for testing only, and is not tracked in a thread-safe
   // way.
   static bool IsHighResolutionTimerInUse();
+
+  // The following two functions are used to report the fraction of elapsed time
+  // that the high resolution timer is activated.
+  // ResetHighResolutionTimerUsage() resets the cumulative usage and starts the
+  // measurement interval and GetHighResolutionTimerUsage() returns the
+  // percentage of time since the reset that the high resolution timer was
+  // activated.

[gab, 2017/06/28 16:39:33]

Also document that Get() is invalid before Reset() was called at least once?
(although your test verify that case, it's undefined to use Get() before Reset()
when the highres timer was activated already)

[stanisc, 2017/06/28 22:28:35]

Done.

+  static void ResetHighResolutionTimerUsage();
+  static double GetHighResolutionTimerUsage();
 #endif

[gab, 2017/06/28 16:39:33]

#endif  // defined(OS_WIN)

(this block is becoming larger and larger and a closing comment is now
justified)

[stanisc, 2017/06/28 22:28:35]

Done.

 
   // Converts an exploded structure representing either the local time or UTC