Make much of the proxy thread-safe with 1 great big lock.

ppapi/shared_impl/proxy_lock.cc

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ppapi/shared_impl/proxy_lock.h"
+
+#include "base/synchronization/lock.h"
+
+namespace ppapi {
+
+base::Lock* ProxyLock::lock_ = NULL;
+
+// static
+void ProxyLock::Acquire() {
+  if (lock_)
+    lock_->Acquire();
+}
+
+// static
+void ProxyLock::Release() {
+  if (lock_)
+    lock_->Release();
+}
+
+// static
+void ProxyLock::Set(base::Lock* lock) {
+  lock_ = lock;
+}
+
+// static
+void ProxyLock::Reset() {
+  Set(NULL);
+}
+
+}  // namespace ppapi