[Thumbnails DB] Add functionality to clear unused on-demand favicons.

components/history/core/browser/expire_history_backend.cc

Index: components/history/core/browser/expire_history_backend.cc
diff --git a/components/history/core/browser/expire_history_backend.cc b/components/history/core/browser/expire_history_backend.cc
index d57a60432afb85c3f74790c13d50d8e7865dd7b9..481af20408b231942de7fd6caec9dd6002063e6f 100644
--- a/components/history/core/browser/expire_history_backend.cc
+++ b/components/history/core/browser/expire_history_backend.cc
@@ -12,6 +12,7 @@
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
+#include "base/feature_list.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
@@ -114,6 +115,10 @@ const int kExpirationDelaySec = 30;
 // iteration, so we want to wait longer before checking to avoid wasting CPU.
 const int kExpirationEmptyDelayMin = 5;
 
+// Feature that enables clearing old on-demand favicons.
+const base::Feature kClearOldOnDemandFavicons{
+    "ClearOldOnDemandFavicons", base::FEATURE_DISABLED_BY_DEFAULT};
+
 }  // namespace
 
 
@@ -300,6 +305,19 @@ void ExpireHistoryBackend::StartExpiringOldStuff(
   // Initialize the queue with all tasks for the first set of iterations.
   InitWorkQueue();
   ScheduleExpire();
+
+  // Remove favicons that are not bound to visits.
+  if (!base::FeatureList::IsEnabled(kClearOldOnDemandFavicons))
+    return;
+  task_runner_->PostDelayedTask(
+      FROM_HERE,
+      base::Bind(&ExpireHistoryBackend::ClearOldOnDemandFavicons,
+                 weak_factory_.GetWeakPtr()),
+      base::TimeDelta::FromSeconds(kExpirationDelaySec));
+}
+
+void ExpireHistoryBackend::ClearOldOnDemandFavicons() {
+  thumb_db_->ClearOldOnDemandFavicons(GetCurrentExpirationTime());
 }
 
 void ExpireHistoryBackend::DeleteFaviconsIfPossible(DeleteEffects* effects) {