Add Precache.Fetch.MinWeight UMA.

components/precache/content/precache_manager.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/content/precache_manager.h"
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram_macros.h"
+#include "base/optional.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/time/time.h"
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_settings.h"
 #include "components/history/core/browser/history_service.h"
 #include "components/precache/core/precache_database.h"
 #include "components/precache/core/precache_switches.h"
 #include "components/precache/core/proto/unfinished_work.pb.h"
 #include "components/prefs/pref_service.h"
 #include "components/sync/driver/sync_service.h"
@@ skipping 238 matching lines @@
 
 void PrecacheManager::OnGetUnfinishedWorkDone(
     std::unique_ptr<PrecacheUnfinishedWork> unfinished_work) {
   // Reset progress on a prefetch that has taken too long to complete.
   if (unfinished_work->has_start_time() &&
       base::Time::Now() -
               base::Time::FromInternalValue(unfinished_work->start_time()) >
           base::TimeDelta::FromHours(6)) {
     PrecacheFetcher::RecordCompletionStatistics(
         *unfinished_work, unfinished_work->top_host_size(),
-        unfinished_work->resource_size());
+        unfinished_work->resource_size(), base::nullopt);

[jamartin, 2017/02/22 22:54:07]

When does this case happen? When we haven't precached everything that we should
nor reached any of the caps yet the precaching session has lasted at least 6
hours? If yes, I wonder if we should still report the min_weight, since it is
still representative of the last resource precached by this client.

[twifkak, 2017/02/23 23:28:41]

Yes. The problem is that the weights aren't in the unfinished_work (just the
weight_ratios), so I'd need to add an API hook and some extra work to compute
that. I presume that the fraction of precaches that hit this timeout is tiny
enough that this isn't worth the bother.

     unfinished_work.reset(new PrecacheUnfinishedWork);
   }
   // If this prefetch is new, set the start time.
   if (!unfinished_work->has_start_time())
     unfinished_work->set_start_time(base::Time::Now().ToInternalValue());
   unfinished_work_ = std::move(unfinished_work);
   bool needs_top_hosts = unfinished_work_->top_host_size() == 0;
 
   if (IsInExperimentGroup()) {
     BrowserThread::PostTask(
@@ skipping 209 matching lines @@
       this));
   precache_fetcher_->Start();
 }
 
 void PrecacheManager::OnHostsReceivedThenDone(
     const history::TopHostsList& host_counts) {
   OnDone();
 }
 
 }  // namespace precache