Adding the ability to use a simulated clock for unit tests.

webrtc/base/timeutils.h

Index: webrtc/base/timeutils.h
diff --git a/webrtc/base/timeutils.h b/webrtc/base/timeutils.h
index 4af0d9538f058f9d969f954cd9a7fb5620463fd7..180d3e6e675d38f75038b2849c64a54ab05686ce 100644
--- a/webrtc/base/timeutils.h
+++ b/webrtc/base/timeutils.h
@@ -31,6 +31,19 @@ static const int64_t kNumNanosecsPerMicrosec =
 
 typedef uint32_t TimeStamp;
 
+class ClockInterface {
+ public:
+  virtual ~ClockInterface() {}
+  virtual uint64_t TimeNanos() const = 0;
+};

[pthatcher1, 2016/05/24 18:05:46]

Can you put a TODO to move this into a clock.h?  In fact, could you add clock.h
now and just include this file, so that new code can start using it and old code
can start moving over?  

Can you also make a TODO to remove Timing in timing.h, since it will no longer
be needed?

[Taylor Brandstetter, 2016/05/24 21:48:00]

What do you mean by "new code start moving over"? What are they moving to?

[pthatcher1, 2016/05/26 17:48:38]

I mean we replace all uses of Timing with ClockInterface and delete Timing.

+
+// Sets the global source of time. This is useful mainly for unit tests.
+// SetClock(nullptr) should be called before the ClockInterface is deleted.
+// This method is not thread-safe; it should only be used when no other thread
+// is running (for example, at the start/end of a unit test, or start/end of
+// main()).
+void SetClock(ClockInterface* clock);
+
 // Returns the current time in milliseconds in 32 bits.
 uint32_t Time32();