FileAPI: Compare expected modification time with delta on file read

storage/browser/fileapi/file_stream_reader.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 "storage/browser/fileapi/file_stream_reader.h"
 
 #include "base/time/time.h"
 
 namespace storage {
 
+// Int64->double->int64 conversions (e.g. through Blink) may lose some
+// precision in the microsecond range. Allow 10us delta.
+const int kModificationTimeAllowedDeltaMicroseconds = 10;
+
 // Verify if the underlying file has not been modified.
 bool FileStreamReader::VerifySnapshotTime(
     const base::Time& expected_modification_time,
     const base::File::Info& file_info) {
   return expected_modification_time.is_null() ||
-         expected_modification_time.ToTimeT() ==
-             file_info.last_modified.ToTimeT();
+         (expected_modification_time - file_info.last_modified)
+                 .magnitude()
+                 .InMicroseconds() < kModificationTimeAllowedDeltaMicroseconds;
 }
 
 }  // namespace storage