Make base::ReadFileToString() return false on I/O error.

base/file_util.cc

 // Copyright (c) 2012 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/file_util.h"
 
 #if defined(OS_WIN)
 #include <io.h>
 #endif
 #include <stdio.h>
@@ skipping 139 matching lines @@
     if (contents)
       contents->append(buf, std::min(len, max_size - size));
 
     if ((max_size - size) < len) {
       read_status = false;
       break;
     }
 
     size += len;
   }
+  read_status = read_status && !ferror(file);
   CloseFile(file);
 
   return read_status;
 }
 
 bool ReadFileToString(const FilePath& path, std::string* contents) {
   return ReadFileToString(path, contents, std::numeric_limits<size_t>::max());
 }
 
 bool IsDirectoryEmpty(const FilePath& dir_path) {
@@ skipping 80 matching lines @@
     if (!PathExists(new_path) &&
         (!have_suffix || !PathExists(FilePath(new_path.value() + suffix)))) {
       return count;
     }
   }
 
   return -1;
 }
 
 }  // namespace base