Refactor RtpSender and SSRCDatabase a bit.

webrtc/modules/rtp_rtcp/source/ssrc_database.cc

Index: webrtc/modules/rtp_rtcp/source/ssrc_database.cc
diff --git a/webrtc/modules/rtp_rtcp/source/ssrc_database.cc b/webrtc/modules/rtp_rtcp/source/ssrc_database.cc
index fb02b7ef12cd12f785fd18ed331e1407d3fd38c4..7c06dccab97a8df6d8d764b299815824e21bbe07 100644
--- a/webrtc/modules/rtp_rtcp/source/ssrc_database.cc
+++ b/webrtc/modules/rtp_rtcp/source/ssrc_database.cc
@@ -11,15 +11,9 @@
 #include "webrtc/modules/rtp_rtcp/source/ssrc_database.h"
 
 #include "webrtc/base/checks.h"
-#include "webrtc/system_wrappers/include/clock.h"
-#include "webrtc/system_wrappers/include/critical_section_wrapper.h"
+#include "webrtc/system_wrappers/include/tick_util.h"
 
 namespace webrtc {
-namespace {
-uint64_t Seed() {
-  return Clock::GetRealTimeClock()->TimeInMicroseconds();
-}
-}  // namespace
 
 SSRCDatabase* SSRCDatabase::GetSSRCDatabase() {
   return GetStaticInstance<SSRCDatabase>(kAddRef);
@@ -30,7 +24,7 @@ void SSRCDatabase::ReturnSSRCDatabase() {
 }
 
 uint32_t SSRCDatabase::CreateSSRC() {
-  CriticalSectionScoped lock(crit_.get());
+  rtc::CritScope lock(&crit_);
 
   while (true) {  // Try until get a new ssrc.
     // 0 and 0xffffffff are invalid values for SSRC.
@@ -42,19 +36,27 @@ uint32_t SSRCDatabase::CreateSSRC() {
 }
 
 void SSRCDatabase::RegisterSSRC(uint32_t ssrc) {
-  CriticalSectionScoped lock(crit_.get());
+  rtc::CritScope lock(&crit_);
   ssrcs_.insert(ssrc);
 }
 
 void SSRCDatabase::ReturnSSRC(uint32_t ssrc) {
-  CriticalSectionScoped lock(crit_.get());
+  rtc::CritScope lock(&crit_);
   ssrcs_.erase(ssrc);
 }
 
-SSRCDatabase::SSRCDatabase()
-    : crit_(CriticalSectionWrapper::CreateCriticalSection()), random_(Seed()) {}
-
-SSRCDatabase::~SSRCDatabase() {
-}
+// For initializing the random seed, we don't use TimeInMicroseconds() since it
+// can return 0 on Mac if we're  called early on during process startup (e.g.
+// in tests).  This is because when the tick count gets converted into
+// microseconds, we can end up multiplying with 0 and end up with a seed of 0.
+// TODO(tommi): Make initialization of Random possible without having to provide
+// a seed.  Random could use functionality in webrtc/base* to generate a seed
+// and we should probably have a special function who's purpose
+// is clear and not just a generic tick count since the implementation varies
+// from platform to platform.
+// * Can't be TickTime since it is in system_wrappers.
+SSRCDatabase::SSRCDatabase() : random_(TickTime::Now().Ticks()) {}
+
+SSRCDatabase::~SSRCDatabase() {}
 
 }  // namespace webrtc