Remove obviously unneeded forward declarations from headers under src/{app,base,net}.

base/linux_util.h

 // Copyright (c) 2010 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 BASE_LINUX_UTIL_H_
 #define BASE_LINUX_UTIL_H_
 #pragma once
 
 #include <stdint.h>
 #include <sys/types.h>
 
 #include <string>
 
-class FilePath;
-
 namespace base {
 
 static const char kFindInodeSwitch[] = "--find-inode";
 
 // Get the Linux Distro if we can, or return "Unknown", similar to
 // GetWinVersion() in base/win_util.h.
 std::string GetLinuxDistro();
 
 // Return the inode number for the UNIX domain socket |fd|.
 bool FileDescriptorGetInode(ino_t* inode_out, int fd);
 
 // Find the process which holds the given socket, named by inode number. If
 // multiple processes hold the socket, this function returns false.
 bool FindProcessHoldingSocket(pid_t* pid_out, ino_t socket_inode);
 
 // For a given process |pid|, look through all its threads and find the first
 // thread with /proc/[pid]/task/[thread_id]/syscall whose first N bytes matches
 // |expected_data|, where N is the length of |expected_data|.
 // Returns the thread id or -1 on error.
 pid_t FindThreadIDWithSyscall(pid_t pid, const std::string& expected_data);
 
 }  // namespace base
 
 #endif  // BASE_LINUX_UTIL_H_