Fix error checking for mmap() for POSIX shared memory.

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>
 
@@ skipping 196 matching lines @@
 bool SharedMemory::Map(size_t bytes) {
   if (mapped_file_ == -1)
     return false;
 
   memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
                  MAP_SHARED, mapped_file_, 0);
 
   if (memory_)
     max_size_ = bytes;
 
-  return (memory_ != NULL);
+  bool mmap_succeeded = (memory_ != (void*)-1);
+  DCHECK(mmap_succeeded) << "Call to mmap failed, errno=" << errno;
+  return mmap_succeeded;
 }
 
 bool SharedMemory::Unmap() {
   if (memory_ == NULL)
     return false;
 
   munmap(memory_, max_size_);
   memory_ = NULL;
   max_size_ = 0;
   return true;
@@ skipping 41 matching lines @@
 
 void SharedMemory::Lock() {
   LockOrUnlockCommon(F_LOCK);
 }
 
 void SharedMemory::Unlock() {
   LockOrUnlockCommon(F_ULOCK);
 }
 
 }  // namespace base