Limit InterProcessTimeTicksConverter to platforms that require it

base/time/time.h

Index: base/time/time.h
diff --git a/base/time/time.h b/base/time/time.h
index d51cf485694ac2256d59b27d87e520acdd898171..13e6a6cc88abb04c9dff5963e62a2b64a98dbde2 100644
--- a/base/time/time.h
+++ b/base/time/time.h
@@ -707,6 +707,12 @@ class BASE_EXPORT TimeTicks : public time_internal::TimeBase<TimeTicks> {
   // clock will be used instead.
   static bool IsHighResolution();
 
+  // Returns true if tick clock is consistent across processes meaning that
+  // tick counts taken on different processes can be safely compared with one
+  // another. Time values from different threads that differ 1 tick have an

[charliea (OOO until 10-5), 2016/06/29 22:38:54]

A couple suggestions:

1) s/tick clock/TimeTicks
2) Add a comma after processes
3) s/tick counts/timestamps
4) I'd change that last sentence to something like:

(Note that, even on platforms where this returns true, time values from
different threads that are within one tick of each other must be considered to
have an ambiguous ordering.)

[majidvp, 2016/07/05 01:45:37]

Done.

+  // ambiguous ordering.
+  static bool IsConsistentAcrossProcesses();

[charliea (OOO until 10-5), 2016/06/29 22:38:54]

It looks like, in all cases, IsConsistentAcrossProcesses == IsHighResolution().
Should we just provide an implementation in time.cc?

[majidvp, 2016/07/05 01:45:37]

This is true but that should be seen as a "coincidence" not the rule. I am
afraid if we move it into time.cc it may be seen as a rule and thus be a bit
confusing. Given that this method's exists only to document the semantic of
consistency across processes on different platforms I prefer to avoid any
confusion specially that it won't buy us much if we move it up.
 

[charliea (OOO until 10-5), 2016/07/06 17:43:52]

Acknowledged.

+
 #if defined(OS_WIN)
   // Translates an absolute QPC timestamp into a TimeTicks value. The returned
   // value has the same origin as Now(). Do NOT attempt to use this if