[OfflinePages] Adds TimeToStart UMA for background load requests.

components/offline_pages/background/request_coordinator.cc

 // Copyright 2016 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/offline_pages/background/request_coordinator.h"
 
 #include <limits>
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 56 matching lines @@
     // one to record samples in seconds rather than milliseconds.
     base::HistogramBase* histogram = base::Histogram::FactoryGet(
         AddHistogramSuffix(client_id, "OfflinePages.Background.TimeToSaved"),
         kMinDurationSeconds, kMaxDurationSeconds, kDurationBuckets,
         base::HistogramBase::kUmaTargetedHistogramFlag);
     base::TimeDelta duration = base::Time::Now() - request_creation_time;
     histogram->Add(duration.InSeconds());
   }
 }
 
+void RecordStartTimeUMA(const SavePageRequest& request) {
+  std::string histogram_name("OfflinePages.Background.TimeToStart");
+  if (base::SysInfo::IsLowEndDevice()) {
+    histogram_name += ".Svelte";
+  }
+
+  // The histogram below is an expansion of the UMA_HISTOGRAM_CUSTOM_TIMES
+  // macro adapted to allow for a dynamically suffixed histogram name.
+  // Note: The factory creates and owns the histogram.
+  base::HistogramBase* histogram = base::Histogram::FactoryTimeGet(
+      AddHistogramSuffix(request.client_id(), histogram_name.c_str()),
+      base::TimeDelta::FromMilliseconds(100), base::TimeDelta::FromDays(7), 50,

[Dmitry Titov, 2016/10/21 18:30:25]

This will have second bucket that would take everything from 100ms to >3hrs. And
50 is a good number of buckets already. Would log scale help here? I think we
want more resolution in the first couple hours and then less resolution...

[dougarnett, 2016/10/21 23:16:38]

I thought this one would give exponential buckets vs. using
LinearHistogram::FactoryTimeGet. I will double check the reference I used.

[dougarnett, 2016/10/21 23:28:52]

Code doc here:
https://cs.chromium.org/chromium/src/base/metrics/histogram_macros.h?rcl=0&l=136

OfflinePages.SavePageTime uses this and is not linear. I can certainly drop the
max though. 

+      base::HistogramBase::kUmaTargetedHistogramFlag);
+  base::TimeDelta duration = base::Time::Now() - request.creation_time();
+  histogram->AddTime(duration);
+}
+
 void RecordCancelTimeUMA(const SavePageRequest& canceled_request) {
   // Using regular histogram (with dynamic suffix) rather than time-oriented
   // one to record samples in seconds rather than milliseconds.
   base::HistogramBase* histogram = base::Histogram::FactoryGet(
       AddHistogramSuffix(canceled_request.client_id(),
                          "OfflinePages.Background.TimeToCanceled"),
       kMinDurationSeconds, kMaxDurationSeconds, kDurationBuckets,
       base::HistogramBase::kUmaTargetedHistogramFlag);
   base::TimeDelta duration =
       base::Time::Now() - canceled_request.creation_time();
@@ skipping 453 matching lines @@
   GetOffliner();
   if (!offliner_) {
     DVLOG(0) << "Unable to create Offliner. "
              << "Cannot background offline page.";
     return;
   }
 
   DCHECK(!is_busy_);
   is_busy_ = true;
 
+  // Record start time if this is first attempt.
+  if (request.started_attempt_count() == 0) {
+    RecordStartTimeUMA(request);
+  }
+
   // Mark attempt started in the database and start offliner when completed.
   queue_->MarkAttemptStarted(
       request.request_id(),
       base::Bind(&RequestCoordinator::StartOffliner,
                  weak_ptr_factory_.GetWeakPtr(), request.request_id(),
                  request.client_id().name_space));
 }
 
 void RequestCoordinator::StartOffliner(
     int64_t request_id,
@@ skipping 190 matching lines @@
 
 ClientPolicyController* RequestCoordinator::GetPolicyController() {
   return policy_controller_.get();
 }
 
 void RequestCoordinator::Shutdown() {
   network_quality_estimator_ = nullptr;
 }
 
 }  // namespace offline_pages