Revert of Delete class SSRCDatabase, and its global ssrc registry.

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
new file mode 100644
index 0000000000000000000000000000000000000000..a96d05db468f0309740b8dca2cdc617ffd310daf
--- /dev/null
+++ b/webrtc/modules/rtp_rtcp/source/ssrc_database.cc
@@ -0,0 +1,51 @@
+/*
+ *  Copyright (c) 2011 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.
+ */
+
+#include "webrtc/modules/rtp_rtcp/source/ssrc_database.h"
+#include "webrtc/base/timeutils.h"
+#include "webrtc/base/checks.h"
+
+namespace webrtc {
+
+SSRCDatabase* SSRCDatabase::GetSSRCDatabase() {
+  return GetStaticInstance<SSRCDatabase>(kAddRef);
+}
+
+void SSRCDatabase::ReturnSSRCDatabase() {
+  GetStaticInstance<SSRCDatabase>(kRelease);
+}
+
+uint32_t SSRCDatabase::CreateSSRC() {
+  rtc::CritScope lock(&crit_);
+
+  while (true) {  // Try until get a new ssrc.
+    // 0 and 0xffffffff are invalid values for SSRC.
+    uint32_t ssrc = random_.Rand(1u, 0xfffffffe);
+    if (ssrcs_.insert(ssrc).second) {
+      return ssrc;
+    }
+  }
+}
+
+void SSRCDatabase::RegisterSSRC(uint32_t ssrc) {
+  rtc::CritScope lock(&crit_);
+  ssrcs_.insert(ssrc);
+}
+
+void SSRCDatabase::ReturnSSRC(uint32_t ssrc) {
+  rtc::CritScope lock(&crit_);
+  ssrcs_.erase(ssrc);
+}
+
+SSRCDatabase::SSRCDatabase() : random_(rtc::TimeMicros()) {}
+
+SSRCDatabase::~SSRCDatabase() {}
+
+}  // namespace webrtc