Mojo: Make GetDefault{AsyncWaiter,Logger} static methods of Environment.

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"
 
+struct MojoAsyncWaiter;
+struct MojoLogger;
+
 namespace mojo {
 
-// This class must be instantiated before using any Mojo C++ APIs.
+// Other parts of the Mojo C++ APIs use the *static* methods of this class.
+//
+// The "standalone" implementation of this class requires that this class (in
+// the lib/ subdirectory) be instantiated (and remain so) while using the Mojo
+// C++ APIs. I.e., the static methods depend on things set up by the constructor
+// and torn down by the destructor.
+//
+// Other implementations may not have this requirement.
 class Environment {
  public:
   Environment();
+  // This constructor allows the standard implementations to be overridden (set
+  // a parameter to null to get the standard implementation).
+  Environment(const MojoAsyncWaiter* default_async_waiter,
+              const MojoLogger* default_logger);
   ~Environment();
 
-  // Note: Not thread-safe; the default logger must not be used concurrently.
-  static void SetMinimumLogLevel(MojoLogLevel minimum_log_level);
+  static const MojoAsyncWaiter* GetDefaultAsyncWaiter();
+  static const MojoLogger* GetDefaultLogger();
 
  private:
   MOJO_DISALLOW_COPY_AND_ASSIGN(Environment);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_ENVIRONMENT_ENVIRONMENT_H_