Add Precache.Fetch.ResponseBytes.Daily.

components/precache/core/precache_fetcher.cc

Index: components/precache/core/precache_fetcher.cc
diff --git a/components/precache/core/precache_fetcher.cc b/components/precache/core/precache_fetcher.cc
index bab9bc580b1bc06ae111b212dc253cf0e62cdcf1..1cbf787acf2612f45b6c2dcd80a7d371a61c03d6 100644
--- a/components/precache/core/precache_fetcher.cc
+++ b/components/precache/core/precache_fetcher.cc
@@ -718,6 +718,12 @@ void PrecacheFetcher::OnQuotaInfoRetrieved(const PrecacheQuota& quota) {
   quota_ = quota;
   base::Time time_now = base::Time::Now();
   if (IsQuotaTimeExpired(quota_, time_now)) {
+    UMA_HISTOGRAM_CUSTOM_COUNTS(
+        "Precache.Fetch.ResponseBytes.Daily",
+        unfinished_work_->config_settings().daily_quota_total() -
+            quota_.remaining(),

[jamartin, 2017/03/07 21:10:12]

(opt) It would be nice to have a bit more documentation in the Quota proto. It
took me a while to figure out the meaning of the fields and how they were
supposed to be used.

[twifkak, 2017/03/07 21:45:09]

Done.

+        1, kMaxResponseBytes, 100);

[jamartin, 2017/03/07 21:10:12]

I assume you eyeballed the bucket values and they make sense for this case,
right?

[twifkak, 2017/03/07 21:45:09]

Yes. The max is 500MB, which is more than enough for the 40MB/day we allot. The
bucket config is the same as the other ResponseBytes histos, and provide enough
detail for those (which sit around the 10MB range).

+
     // This is a new day. Update daily quota, that starts today and expires by
     // end of today.

[jamartin, 2017/03/07 21:10:12]

Keep the comment at the beginning of the if block.

[twifkak, 2017/03/07 21:45:09]

Done.

     quota_.set_start_time(time_now.LocalMidnight().ToInternalValue());