[NTP Snippets] Add UMA for database load time

components/ntp_snippets/remote/ntp_snippets_service.cc

 // Copyright 2015 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/ntp_snippets/remote/ntp_snippets_service.h"
 
 #include <algorithm>
 #include <iterator>
 #include <utility>
 
@@ skipping 195 matching lines @@
     EnterState(State::ERROR_OCCURRED);
     UpdateAllCategoryStatus(CategoryStatus::LOADING_ERROR);
     return;
   }
 
   database_->SetErrorCallback(base::Bind(&NTPSnippetsService::OnDatabaseError,
                                          base::Unretained(this)));
 
   // We transition to other states while finalizing the initialization, when the
   // database is done loading.
+  database_load_start_ = base::TimeTicks::Now();
   database_->LoadSnippets(base::Bind(&NTPSnippetsService::OnDatabaseLoaded,
                                      base::Unretained(this)));
 }
 
 NTPSnippetsService::~NTPSnippetsService() = default;
 
 // static
 void NTPSnippetsService::RegisterProfilePrefs(PrefRegistrySimple* registry) {
   // TODO(treib): Add cleanup logic for prefs::kSnippetHosts, then remove it
   // completely after M56.
@@ skipping 239 matching lines @@
   // provided to |image_fetcher_| (OnSnippetImageDecodedFromNetwork()).
   database_->SaveImage(id_within_category, image_data);
 }
 
 void NTPSnippetsService::OnDatabaseLoaded(NTPSnippet::PtrVector snippets) {
   if (state_ == State::ERROR_OCCURRED)
     return;
   DCHECK(state_ == State::NOT_INITED);
   DCHECK(base::ContainsKey(categories_, articles_category_));
 
+  base::TimeDelta database_load_time =
+      base::TimeTicks::Now() - database_load_start_;
+  UMA_HISTOGRAM_MEDIUM_TIMES("NewTabPage.Snippets.DatabaseLoadTime",
+                             database_load_time);
+
   NTPSnippet::PtrVector to_delete;
   for (std::unique_ptr<NTPSnippet>& snippet : snippets) {
     Category snippet_category =
         category_factory()->FromRemoteCategory(snippet->remote_category_id());
     // We should already know about the category.
     if (!base::ContainsKey(categories_, snippet_category)) {
       DLOG(WARNING) << "Loaded a suggestion for unknown category "
                     << snippet_category << " from the DB; deleting";
       to_delete.emplace_back(std::move(snippet));
       continue;
@@ skipping 617 matching lines @@
 }
 
 NTPSnippetsService::CategoryContent::CategoryContent() = default;
 NTPSnippetsService::CategoryContent::CategoryContent(CategoryContent&&) =
     default;
 NTPSnippetsService::CategoryContent::~CategoryContent() = default;
 NTPSnippetsService::CategoryContent& NTPSnippetsService::CategoryContent::
 operator=(CategoryContent&&) = default;
 
 }  // namespace ntp_snippets