Mojo: Add GetMinimumLogLevel() to the logger interface.

mojo/public/cpp/environment/environment.h

 // Copyright 2014 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.
 
 #ifndef MOJO_PUBLIC_CPP_ENVIRONMENT_ENVIRONMENT_H_
 #define MOJO_PUBLIC_CPP_ENVIRONMENT_ENVIRONMENT_H_
 
+#include "mojo/public/c/environment/logger.h"
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
 
-// This class must be instantiated before using any Mojo APIs.
+// This class must be instantiated before using any Mojo C++ APIs.
 class Environment {
  public:
   Environment();
   ~Environment();
 
+  // Note: Not thread-safe; the default logger must not be used concurrently.
+  static void SetMinimumLogLevel(MojoLogLevel minimum_log_level);
+
  private:
   MOJO_DISALLOW_COPY_AND_ASSIGN(Environment);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_ENVIRONMENT_ENVIRONMENT_H_