Add log for when timestamp map size hits limit

BUG=1134755
TEST=CQ

Change-Id: Ic1a50d2e944d09d7795ea01609a5a56b2a5207ba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2460830
Auto-Submit: Risan <risan@chromium.org>
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815334}

chrome/browser/chromeos/arc/file_system_watcher/arc_file_system_watcher_service.cc

@@ -124,8 +124,10 @@ TimestampMap BuildTimestampMap(base::FilePath cros_dir,
                                   base::FileEnumerator::FILES);
   for (base::FilePath cros_path = enumerator.Next(); !cros_path.empty();
        cros_path = enumerator.Next()) {
-    if (timestamp_map.size() >= kMaxTimestampMapSize)
+    if (timestamp_map.size() >= kMaxTimestampMapSize) {
+      LOG(WARNING) << "The timestamp map size exceeds max limit";
       break;
+    }
     // Skip non-media files for efficiency.
     if (!HasAndroidSupportedMediaExtension(cros_path))
       continue;