Use TimeTicks instead of Time for measuring elapsed time

TimeTicks is preferred for measuring time, when time isn't being measured
across restarts. These were the only two cases I found under
components/offline_pages that could be converted to TimeTicks.

Change-Id: I627698de121cdda5d7853e0d92f7032ade524a40
Reviewed-on: https://chromium-review.googlesource.com/c/1364080
Commit-Queue: Dan H <harringtond@google.com>
Reviewed-by: Carlos Knippschild <carlosk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615604}

components/offline_pages/core/offline_page_metadata_store.cc

@@ -13,9 +13,7 @@
 #include "base/sequenced_task_runner.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/utf_string_conversions.h"
-#include "base/time/clock.h"
 #include "components/offline_pages/core/client_namespace_constants.h"
-#include "components/offline_pages/core/offline_clock.h"
 #include "components/offline_pages/core/offline_page_item.h"
 #include "components/offline_pages/core/offline_store_types.h"
 #include "components/offline_pages/core/offline_store_utils.h"
@@ -413,7 +411,7 @@ void OfflinePageMetadataStore::InitializeInternal(
   if (!last_closing_time_.is_null()) {
     ReportStoreEvent(OfflinePagesStoreEvent::kReopened);
     UMA_HISTOGRAM_CUSTOM_TIMES("OfflinePages.SQLStorage.TimeFromCloseToOpen",
-                               OfflineClock()->Now() - last_closing_time_,
+                               base::TimeTicks::Now() - last_closing_time_,
                                base::TimeDelta::FromMilliseconds(10),
                                base::TimeDelta::FromMinutes(10),
                                50 /* buckets */);
@@ -468,7 +466,7 @@ void OfflinePageMetadataStore::CloseInternal() {
   }
   TRACE_EVENT_ASYNC_STEP_PAST0("offline_pages", "Metadata Store", this, "Open");
 
-  last_closing_time_ = OfflineClock()->Now();
+  last_closing_time_ = base::TimeTicks::Now();
   ReportStoreEvent(OfflinePagesStoreEvent::kClosed);
 
   state_ = StoreState::NOT_LOADED;

components/offline_pages/core/offline_page_metadata_store.h

@@ -227,7 +227,7 @@ class OfflinePageMetadataStore {
   std::vector<base::OnceClosure> pending_commands_;
 
   // Time of the last time the store was closed. Kept for metrics reporting.
-  base::Time last_closing_time_;
+  base::TimeTicks last_closing_time_;
 
   base::WeakPtrFactory<OfflinePageMetadataStore> weak_ptr_factory_;
   base::WeakPtrFactory<OfflinePageMetadataStore> closing_weak_ptr_factory_;

components/offline_pages/core/prefetch/store/prefetch_store.cc

@@ -115,7 +115,7 @@ void PrefetchStore::Initialize(base::OnceClosure pending_command) {
   if (!last_closing_time_.is_null()) {
     ReportStoreEvent(OfflinePagesStoreEvent::kReopened);
     UMA_HISTOGRAM_CUSTOM_TIMES("OfflinePages.PrefetchStore.TimeFromCloseToOpen",
-                               base::Time::Now() - last_closing_time_,
+                               base::TimeTicks::Now() - last_closing_time_,
                                base::TimeDelta::FromMilliseconds(10),
                                base::TimeDelta::FromMinutes(10),
                                50 /* buckets */);
@@ -167,7 +167,7 @@ void PrefetchStore::CloseInternal() {
   }
   TRACE_EVENT_ASYNC_STEP_PAST0("offline_pages", "Prefetch Store", this, "Open");
 
-  last_closing_time_ = base::Time::Now();
+  last_closing_time_ = base::TimeTicks::Now();
   ReportStoreEvent(OfflinePagesStoreEvent::kClosed);
 
   initialization_status_ = InitializationStatus::NOT_INITIALIZED;

components/offline_pages/core/prefetch/store/prefetch_store.h

@@ -173,7 +173,7 @@ class PrefetchStore {
   InitializationStatus initialization_status_;
 
   // Time of the last time the store was closed. Kept for metrics reporting.
-  base::Time last_closing_time_;
+  base::TimeTicks last_closing_time_;
 
   // Weak pointer to control the callback.
   base::WeakPtrFactory<PrefetchStore> weak_ptr_factory_;