Return true when file size is zero.

base/test/test_file_util_mac.cc

 // Copyright (c) 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/test/test_file_util.h"
 
 #include <sys/mman.h>
 #include <errno.h>
 #include "base/logging.h"
 #include "base/file_util.h"
 
 namespace file_util {
 
 bool EvictFileFromSystemCache(const FilePath& file) {
   // There aren't any really direct ways to purge a file from the UBC.  From
   // talking with Amit Singh, the safest is to mmap the file with MAP_FILE (the
   // default) + MAP_SHARED, then do an msync to invalidate the memory.  The next
   // open should then have to load the file from disk.
 
+  int64 length;
+  if (!file_util::GetFileSize(file, &length)) {
+    LOG(ERROR) << "failed to get size of " << file.value();
+    return false;
+  }
+
+  // When a file is empty, we do not need to evict it from cache.
+  // In fact, an attempt to map it to memory will result in error.
+  if (length == 0) {
+    LOG(WARNING) << "file size is zero, will not attempt to map to memory";
+    return true;
+  }
+
   file_util::MemoryMappedFile mapped_file;
   if (!mapped_file.Initialize(file)) {
-    DLOG(WARNING) << "failed to memory map " << file.value();
+    LOG(WARNING) << "failed to memory map " << file.value();
     return false;
   }
 
   if (msync(const_cast<uint8*>(mapped_file.data()), mapped_file.length(),
             MS_INVALIDATE) != 0) {
-    DLOG(WARNING) << "failed to invalidate memory map of " << file.value()
+    LOG(WARNING) << "failed to invalidate memory map of " << file.value()
         << ", errno: " << errno;
     return false;
   }
 
   return true;
 }
 
 }  // namespace file_util