Cleanup remaining class/struct fwd declarations

mojo/edk/test/multiprocess_test_helper.h

 // Copyright 2013 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_EDK_TEST_MULTIPROCESS_TEST_HELPER_H_
 #define MOJO_EDK_TEST_MULTIPROCESS_TEST_HELPER_H_
 
 #include <string>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/process/process.h"
 #include "base/test/multiprocess_test.h"
 #include "base/test/test_timeouts.h"
 #include "mojo/edk/embedder/embedder.h"
 #include "mojo/public/cpp/system/message_pipe.h"
 #include "testing/multiprocess_func_list.h"
 
 namespace mojo {
 
 namespace edk {
-class PlatformChannelPair;
 
 namespace test {
 
 class MultiprocessTestHelper {
  public:
   using HandlerCallback = base::Callback<void(ScopedMessagePipeHandle)>;
 
   enum class LaunchType {
     // Launch the child process as a child in the mojo system.
     CHILD,
@@ skipping 68 matching lines @@
   std::string peer_token_;
 
   DISALLOW_COPY_AND_ASSIGN(MultiprocessTestHelper);
 };
 
 }  // namespace test
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_TEST_MULTIPROCESS_TEST_HELPER_H_