Fix error handling in POSIX version of the base::File::GetLength.

net/disk_cache/blockfile/file_ios.cc

 // Copyright 2014 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 "net/disk_cache/blockfile/file.h"
 
 #include <limits.h>
 #include <stdint.h>
 
 #include <limits>
@@ skipping 240 matching lines @@
   if (length > std::numeric_limits<uint32_t>::max())
     return false;
 
   return base_file_.SetLength(length);
 }
 
 size_t File::GetLength() {
   DCHECK(base_file_.IsValid());
   int64_t len = base_file_.GetLength();
 
+  if (len < 0)
+    return 0;
   if (len > static_cast<int64_t>(std::numeric_limits<uint32_t>::max()))
     return std::numeric_limits<uint32_t>::max();
 
   return static_cast<size_t>(len);
 }
 
 // Static.
 void File::WaitForPendingIO(int* num_pending_io) {
   // We may be running unit tests so we should allow be able to reset the
   // message loop.
@@ skipping 21 matching lines @@
     return false;
 
   GetFileInFlightIO()->PostWrite(this, buffer, buffer_len, offset, callback);
 
   if (completed)
     *completed = false;
   return true;
 }
 
 }  // namespace disk_cache