Report Precache.TimeSinceLastPrecache

components/precache/core/precache_database.cc

Index: components/precache/core/precache_database.cc
diff --git a/components/precache/core/precache_database.cc b/components/precache/core/precache_database.cc
index e9d53ecad16d8bc30ebd4415013430d1bd131dda..878072ac8741d6f8c88df102ffb2f7d79cc42702 100644
--- a/components/precache/core/precache_database.cc
+++ b/components/precache/core/precache_database.cc
@@ -90,6 +90,30 @@ void PrecacheDatabase::ClearHistory() {
   Flush();
 }
 
+void PrecacheDatabase::SetLastPrecacheTimestamp(const base::Time& time) {
+  last_precache_timestamp_ = time;
+
+  if (!IsDatabaseAccessible()) {
+    // Do nothing if unable to access the database.
+    return;
+  }
+
+  buffered_writes_.push_back(
+      base::Bind(&PrecacheSessionTable::SetLastPrecacheTimestamp,
+                 base::Unretained(&precache_session_table_), time));
+  MaybePostFlush();
+}
+
+base::Time PrecacheDatabase::GetLastPrecacheTimestamp() {
+  if (!IsDatabaseAccessible()) {
+    // Use the cached value, possibly not initialized (and hence is_null()).
+    return last_precache_timestamp_;
+  }
+
+  last_precache_timestamp_ = precache_session_table_.GetLastPrecacheTimestamp();
+  return last_precache_timestamp_;
+}
+
 void PrecacheDatabase::RecordURLPrefetch(const GURL& url,
                                          const base::TimeDelta& latency,
                                          const base::Time& fetch_time,
@@ -157,6 +181,8 @@ void PrecacheDatabase::RecordURLNonPrefetch(const GURL& url,
     return;
   }
 
+  RecordTimeSinceLastPrecache(fetch_time);
+
   if (buffered_urls_.find(url.spec()) != buffered_urls_.end()) {
     // If the URL for this fetch is in the write buffer, then flush the write
     // buffer.
@@ -201,6 +227,24 @@ void PrecacheDatabase::RecordURLNonPrefetch(const GURL& url,
   MaybePostFlush();
 }
 
+void PrecacheDatabase::RecordTimeSinceLastPrecache(
+    const base::Time& fetch_time) {
+  if (last_precache_timestamp_.is_null()) {
+    last_precache_timestamp_ =
+        precache_session_table_.GetLastPrecacheTimestamp();
+  }
+  // It could still be null if the DB was not accessible.
+  if (!last_precache_timestamp_.is_null()) {
+    // This is the timespan between the last call to
+    // PrecacheManager::StartPrecaching and the fetch time of a non-precache
+    // URL. Please note that the session started by that call to
+    // PrecacheManager::StartPrecaching may not have precached this particular
+    // URL or even any URL for that matter.
+    UMA_HISTOGRAM_TIMES("Precache.TimeSinceLastPrecache",
+                        fetch_time - last_precache_timestamp_);
+  }
+}
+
 bool PrecacheDatabase::IsDatabaseAccessible() const {
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK(db_);