CacheStorage: Relax index file timestamp DCHECK.

On some platforms the base path timestamp can be a few microseconds
different from the file contained in the directory.  Relax the DCHECK
to permit +/- 10 microseconds difference.

Bug: 1002892
Change-Id: Iebdc1685c5b3e48e674f938bd530a5247caef1e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1847732Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Ben Kelly <wanderview@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703830}

content/browser/cache_storage/legacy/legacy_cache_storage_manager.cc

@@ -70,7 +70,11 @@ int64_t GetCacheStorageSize(const base::FilePath& base_path,
   // have a modified time older than the index's modified time.  Modifying
   // the index should update the directories time as well.  Therefore we
   // should be guaranteed that the time is equal here.
-  DCHECK_EQ(base_path_time, index_time);
+  //
+  // In practice, though, there can be a few microseconds difference on
+  // some operating systems so we can't do an exact DCHECK here.  Instead
+  // we do a fuzzy DCHECK allowing some microseconds difference.
+  DCHECK_LE((index_time - base_path_time).magnitude().InMicroseconds(), 10);
 
   int64_t storage_size = 0;
   for (int i = 0, max = index.cache_size(); i < max; ++i) {