Refactor RtpSender and SSRCDatabase a bit.

webrtc/base/random.h

 /*
  *  Copyright (c) 2015 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.
  */
 
 #ifndef WEBRTC_BASE_RANDOM_H_
 #define WEBRTC_BASE_RANDOM_H_
 
 #include <limits>
 
 #include "webrtc/typedefs.h"
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/checks.h"
 
 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.
   // We need to limit the size to 32 bits to keep the output close to uniform.
   template <typename T>
   T Rand() {
     static_assert(std::numeric_limits<T>::is_integer &&
                       std::numeric_limits<T>::radix == 2 &&
                       std::numeric_limits<T>::digits <= 32,
                   "Rand is only supported for built-in integer types that are "
@@ skipping 39 matching lines @@
 template <>
 double Random::Rand<double>();
 
 // Return pseudo-random boolean value.
 template <>
 bool Random::Rand<bool>();
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_BASE_RANDOM_H_