Precache should cancel when there is user traffic

components/precache/core/precache_fetcher.cc

 // Copyright 2013 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 "components/precache/core/precache_fetcher.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 #include <utility>
@@ skipping 282 matching lines @@
   UMA_HISTOGRAM_CUSTOM_TIMES("Precache.Fetch.TimeToComplete", time_to_fetch,
                              base::TimeDelta::FromSeconds(1),
                              base::TimeDelta::FromHours(4), 50);
 
   // Number of manifests for which we have downloaded all resources.
   int manifests_completed =
       unfinished_work.num_manifest_urls() - remaining_manifest_urls_to_fetch;
 
   // If there are resource URLs left to fetch, the last manifest is not yet
   // completed.
-  if (remaining_resource_urls_to_fetch > 0)
+  if (remaining_resource_urls_to_fetch > 0 && manifests_completed > 0)

[bengr, 2016/07/06 17:04:27]

This seems like it should be a DCHECK. Could you explain why it is ok for this
method to be called when manifests_completed <= 0?

[Raj, 2016/07/06 18:28:23]

hmm. I got this failure in a few of my tests.
Now it is less apparent to me why this would be the case.
I removed this check. Will fix it when I hit such issue again.

     --manifests_completed;
 
   DCHECK_GE(manifests_completed, 0);
   int percent_completed = unfinished_work.num_manifest_urls() == 0
                               ? 0
                               : (static_cast<double>(manifests_completed) /
                                   unfinished_work.num_manifest_urls() * 100);
 
   UMA_HISTOGRAM_PERCENTAGE("Precache.Fetch.PercentCompleted",
                            percent_completed);
@@ skipping 253 matching lines @@
 
 void PrecacheFetcher::UpdateStats(int64_t response_bytes,
                                   int64_t network_response_bytes) {
   unfinished_work_->set_total_bytes(
       unfinished_work_->total_bytes() + response_bytes);
   unfinished_work_->set_network_bytes(
       unfinished_work_->network_bytes() + network_response_bytes);
 }
 
 }  // namespace precache