Port visitedlink tests to Linux. Also make them pass on Linux, which

base/shared_memory_posix.cc

 // Copyright (c) 2006-2008 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.
 
 #include "base/shared_memory.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ skipping 47 matching lines @@
 
 SharedMemory::~SharedMemory() {
   Close();
 }
 
 // static
 bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
   return handle.fd >= 0;
 }
 
+// static
+SharedMemoryHandle SharedMemory::NULLHandle() {
+  return SharedMemoryHandle();
+}
+
 bool SharedMemory::Create(const std::wstring &name, bool read_only,
                           bool open_existing, size_t size) {
   read_only_ = read_only;
 
   int posix_flags = 0;
   posix_flags |= read_only ? O_RDONLY : O_RDWR;
   if (!open_existing || mapped_file_ <= 0)
     posix_flags |= O_CREAT;
 
   if (!CreateOrOpen(name, posix_flags, size))
@@ skipping 223 matching lines @@
 
 void SharedMemory::Unlock() {
   LockOrUnlockCommon(F_ULOCK);
 }
 
 SharedMemoryHandle SharedMemory::handle() const {
   return FileDescriptor(mapped_file_, false);
 }
 
 }  // namespace base