Refactor RtpSender and SSRCDatabase a bit.

webrtc/base/random.h

Index: webrtc/base/random.h
diff --git a/webrtc/base/random.h b/webrtc/base/random.h
index 647b84c9c947b8d11f711012c9deb5e09b151d3f..bd9f4323b22e3aa561c7fae48cb95cd957d5598e 100644
--- a/webrtc/base/random.h
+++ b/webrtc/base/random.h
@@ -21,6 +21,14 @@ namespace webrtc {
 
 class Random {
  public:
+  // TODO(tommi): Change this so that the seed is initialized internally.

[the sun, 2016/02/01 10:41:28]

Please remove this comment. I believe the right design is for the PRNG to *not*
know how to initialize its seed. The PRNG *client* knows how it wants to do
that.

[tommi, 2016/02/01 17:32:03]

Yeah, so, I'm on the fence about that.  On one side I agree on the other, much
of the code has been calling a method that generates a poor quality seed.  If we
could have a special method for generating the seed that's specifically for
that, then I think we should do that.  Knowing what is a good seed for a PRNG is
something I'd expect to be in the area of the PRNG code, but not something all
clients of PRNG should know how to do.

[pbos-webrtc, 2016/02/01 17:59:25]

Sounds like a case for having two constructors where one who doesn't care can
just use the default ctor?

+  // At the moment all callers are calling clock_->TimeInMicroseconds() which
+  // goes through a global clock object (+vtable) and eventually calls
+  // TickTime::Now().Ticks(), which can return a very low value on Mac, which
+  // can result in a seed of 0 after conversion to microseconds.
+  // Instead see if we can use something from webrtc/base that works the same
+  // way across platforms (and is itself more random than the Mac implementation
+  // of TickTime::Now()).
   explicit Random(uint64_t seed);
 
   // Return pseudo-random integer of the specified type.