[omnibox] Revive InMemoryURLIndex restore and save cache time histograms

These histograms were obsoleted recently.

I would like to bring them back to validate the hypothesis that the
HistoryQuickProvider / InMemoryURLIndex cache is not needed.

Details of experiment: go/chrome-omnibox-hqp-ablate-cache-file

Specifically, my theory is that the time it takes to restore + save the
cache file is in the same order of magnitude as it takes to rebuild the
index from the History DB.

The cache causes two known problems:
 1. Saving it is responsible for roughly 10% of shutdown hangs.
 2. Restoring it seems to take a lot of memory.

This CL is a partial revert of:
https://chromium-review.googlesource.com/c/chromium/src/+/2324551

Bug: 750845, 1032679, 1141539
Change-Id: I7e679c0ba602cf48ab10ad0a89bd75bc3dbf5ee6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490148Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819950}

components/omnibox/browser/url_index_private_data.cc

@@ -383,6 +383,7 @@ bool URLIndexPrivateData::DeleteURL(const GURL& url) {
 // static
 scoped_refptr<URLIndexPrivateData> URLIndexPrivateData::RestoreFromFile(
     const base::FilePath& file_path) {
+  base::TimeTicks beginning_time = base::TimeTicks::Now();
   if (!base::PathExists(file_path))
     return nullptr;
   std::string data;
@@ -409,6 +410,8 @@ scoped_refptr<URLIndexPrivateData> URLIndexPrivateData::RestoreFromFile(
   if (!restored_data->RestorePrivateData(index_cache))
     return nullptr;
 
+  UMA_HISTOGRAM_TIMES("History.InMemoryURLIndexRestoreCacheTime",
+                      base::TimeTicks::Now() - beginning_time);
   UMA_HISTOGRAM_COUNTS_1M("History.InMemoryURLHistoryItems",
                           restored_data->history_id_word_map_.size());
   if (restored_data->Empty())
@@ -934,6 +937,7 @@ void URLIndexPrivateData::ResetSearchTermCache() {
 }
 
 bool URLIndexPrivateData::SaveToFile(const base::FilePath& file_path) {
+  base::TimeTicks beginning_time = base::TimeTicks::Now();
   InMemoryURLIndexCacheItem index_cache;
   SavePrivateData(&index_cache);
   std::string data;
@@ -947,6 +951,8 @@ bool URLIndexPrivateData::SaveToFile(const base::FilePath& file_path) {
     LOG(WARNING) << "Failed to write " << file_path.value();
     return false;
   }
+  UMA_HISTOGRAM_TIMES("History.InMemoryURLIndexSaveCacheTime",
+                      base::TimeTicks::Now() - beginning_time);
   return true;
 }
 

tools/metrics/histograms/histograms_xml/history/histograms.xml

@@ -597,7 +597,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="History.InMemoryURLIndexingTime" units="ms"
-    expires_after="2021-03-30">
+    expires_after="2021-06-30">
   <owner>mpearson@chromium.org</owner>
   <owner>ssid@chromium.org</owner>
   <summary>
@@ -606,6 +606,27 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
+<histogram name="History.InMemoryURLIndexRestoreCacheTime" units="ms"
+    expires_after="2021-06-30">
+  <owner>tommycli@chromium.org</owner>
+  <owner>mpearson@chromium.org</owner>
+  <summary>
+    Time to restore the in-memory url index from disk cache. Recorded on profile
+    open.
+  </summary>
+</histogram>
+
+<histogram name="History.InMemoryURLIndexSaveCacheTime" units="ms"
+    expires_after="2021-06-30">
+  <owner>tommycli@chromium.org</owner>
+  <owner>mpearson@chromium.org</owner>
+  <summary>
+    Time to write in-memory url index to disk cache. Recorded once shortly after
+    profile open (after rebuilding the in-memory url index from history) and
+    again upon (clean) shutdown.
+  </summary>
+</histogram>
+
 <histogram name="History.MigrateFailureFromVersion" units="units"
     expires_after="M77">
   <owner>sky@chromium.org</owner>

tools/metrics/histograms/histograms_xml/obsolete_histograms.xml

@@ -27109,33 +27109,6 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
-<histogram name="History.InMemoryURLIndexRestoreCacheTime" units="ms"
-    expires_after="2019-08-30">
-  <obsolete>
-    Removed July 2020.
-  </obsolete>
-  <owner>mpearson@chromium.org</owner>
-  <owner>ssid@chromium.org</owner>
-  <summary>
-    Time to restore the in-memory url index from disk cache. Recorded on profile
-    open.
-  </summary>
-</histogram>
-
-<histogram name="History.InMemoryURLIndexSaveCacheTime" units="ms"
-    expires_after="2019-08-30">
-  <obsolete>
-    Removed July 2020.
-  </obsolete>
-  <owner>mpearson@chromium.org</owner>
-  <owner>ssid@chromium.org</owner>
-  <summary>
-    Time to write in-memory url index to disk cache. Recorded once shortly after
-    profile open (after rebuilding the in-memory url index from history) and
-    again upon (clean) shutdown.
-  </summary>
-</histogram>
-
 <histogram name="History.InMemoryURLWords" units="units" expires_after="M86">
   <obsolete>
     Removed August 2020.