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

webrtc/base/timeutils.h

 /*
  *  Copyright 2005 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 13 matching lines @@
 
 static const int64_t kNumMicrosecsPerMillisec =
     kNumMicrosecsPerSec / kNumMillisecsPerSec;
 static const int64_t kNumNanosecsPerMillisec =
     kNumNanosecsPerSec / kNumMillisecsPerSec;
 static const int64_t kNumNanosecsPerMicrosec =
     kNumNanosecsPerSec / kNumMicrosecsPerSec;
 
 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();
 
 // Returns the current time in milliseconds in 64 bits.
 int64_t Time64();
 
 // Returns the current time in milliseconds.
 // TODO(honghaiz): Returns Time64 once majority of the webrtc code migrates to
 // 64-bit timestamp.
 inline uint32_t Time() {
@@ skipping 51 matching lines @@
 };
 
 // Convert from std::tm, which is relative to 1900-01-01 00:00 to number of
 // seconds from 1970-01-01 00:00 ("epoch").  Don't return time_t since that
 // is still 32 bits on many systems.
 int64_t TmToSeconds(const std::tm& tm);
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_TIMEUTILS_H_