Add missing windows conditions variable

Those are used by generic RW lock implementation.

https://bugs.freedesktop.org/show_bug.cgi?id=96754

webrtc/system_wrappers/source/condition_variable.cc

@@ -0,0 +1,41 @@
+/*
+ *  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/system_wrappers/include/condition_variable_wrapper.h"
+
+#if defined(_WIN32)
+#include <windows.h>
+#include "webrtc/system_wrappers/source/condition_variable_event_win.h"
+#include "webrtc/system_wrappers/source/condition_variable_native_win.h"
+#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
+#include <pthread.h>
+#include "webrtc/system_wrappers/source/condition_variable_posix.h"
+#endif
+
+namespace webrtc {
+
+ConditionVariableWrapper* ConditionVariableWrapper::CreateConditionVariable() {
+#if defined(_WIN32)
+  // Try to create native condition variable implementation.
+  ConditionVariableWrapper* ret_val = ConditionVariableNativeWin::Create();
+  if (!ret_val) {
+    // Native condition variable implementation does not exist. Create generic
+    // condition variable based on events.
+    ret_val = new ConditionVariableEventWin();
+  }
+  return ret_val;
+#elif defined(WEBRTC_LINUX) || defined(WEBRTC_MAC)
+  return ConditionVariablePosix::Create();
+#else
+  return NULL;
+#endif
+}
+
+}  // namespace webrtc