base: Cleanup class/struct forward declarations

base/debug/activity_tracker.h

 // Copyright 2016 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.
 
 // Activity tracking provides a low-overhead method of collecting information
 // about the state of the application for analysis both while it is running
 // and after it has terminated unexpectedly. Its primary purpose is to help
 // locate reasons the browser becomes unresponsive by providing insight into
 // what all the various threads and processes are (or were) doing.
 
@@ skipping 15 matching lines @@
 #include "base/threading/platform_thread.h"
 #include "base/threading/thread_checker.h"
 #include "base/threading/thread_local_storage.h"
 
 namespace base {
 
 struct PendingTask;
 
 class FilePath;
 class Lock;
-class MemoryMappedFile;
 class PlatformThreadHandle;
 class Process;
 class WaitableEvent;
 
 namespace debug {
 
 class ThreadActivityTracker;
 
 
 enum : int {
@@ skipping 610 matching lines @@
   explicit ScopedProcessWaitActivity(const base::Process* process);
  private:
   DISALLOW_COPY_AND_ASSIGN(ScopedProcessWaitActivity);
 };
 #endif
 
 }  // namespace debug
 }  // namespace base
 
 #endif  // BASE_DEBUG_ACTIVITY_TRACKER_H_