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

components/history/core/browser/expire_history_backend.h

 // Copyright (c) 2012 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.
 
 #ifndef COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_
 #define COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_
 
 #include <memory>
 #include <queue>
 #include <set>
 #include <vector>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "components/history/core/browser/history_types.h"
 
 class GURL;
 class TestingProfile;
 
 namespace base {
+struct Feature;
 class SequencedTaskRunner;
 }
 
 namespace history {
 
 class HistoryBackendClient;
 class HistoryBackendNotifier;
 class HistoryDatabase;
 class ThumbnailDatabase;
 
 // Encapsulates visit expiration criteria and type of visits to expire.
 class ExpiringVisitsReader {
  public:
   virtual ~ExpiringVisitsReader() {}
   // Populates |visits| from |db|, using provided |end_time| and |max_visits|
   // cap.
   virtual bool Read(base::Time end_time, HistoryDatabase* db,
                     VisitVector* visits, int max_visits) const = 0;
 };
 
 typedef std::vector<const ExpiringVisitsReader*> ExpiringVisitsReaders;
 
+namespace internal {
+// Feature that enables clearing old on-demand favicons.
+extern const base::Feature kClearOldOnDemandFavicons;
+}  // namespace internal
+
 // Helper component to HistoryBackend that manages expiration and deleting of
 // history.
 //
 // It will automatically start periodically expiring old history once you call
 // StartExpiringOldStuff().
 class ExpireHistoryBackend {
  public:
   // The delegate pointer must be non-null. We will NOT take ownership of it.
   // HistoryBackendClient may be null. The HistoryBackendClient is used when
   // expiring URLS so that we don't remove any URLs or favicons that are
@@ skipping 40 matching lines @@
   // should not save it.
   base::Time GetCurrentExpirationTime() const {
     return base::Time::Now() - expiration_threshold_;
   }
 
  private:
   FRIEND_TEST_ALL_PREFIXES(ExpireHistoryTest, DeleteFaviconsIfPossible);
   FRIEND_TEST_ALL_PREFIXES(ExpireHistoryTest, ExpireSomeOldHistory);
   FRIEND_TEST_ALL_PREFIXES(ExpireHistoryTest, ExpiringVisitsReader);
   FRIEND_TEST_ALL_PREFIXES(ExpireHistoryTest, ExpireSomeOldHistoryWithSource);
+  FRIEND_TEST_ALL_PREFIXES(ExpireHistoryTest,
+                           ClearOldOnDemandFaviconsDoesNotDeleteStarred);
+  FRIEND_TEST_ALL_PREFIXES(ExpireHistoryTest,
+                           ClearOldOnDemandFaviconsDoesDeleteUnstarred);
   friend class ::TestingProfile;
 
   struct DeleteEffects {
     DeleteEffects();
     ~DeleteEffects();
 
     // The time range affected. These can be is_null() to be unbounded in one
     // or both directions.
     base::Time begin_time, end_time;
 
@@ skipping 57 matching lines @@
   //
   // The visits in the given vector should have already been deleted from the
   // database, and the list of affected URLs already be filled into
   // |depenencies->affected_urls|.
   //
   // Starred URLs will not be deleted. The information in the dependencies that
   // DeleteOneURL fills in will be updated, and this function will also delete
   // any now-unused favicons.
   void ExpireURLsForVisits(const VisitVector& visits, DeleteEffects* effects);
 
+  // Clears all old on-demand favicons from thumbnail database.
+  void ClearOldOnDemandFavicons(base::Time expiration_threshold);

[pkotwicz, 2017/07/07 00:42:38]

Nit: Match the function order in the .cc and the .h file

[jkrcal, 2017/07/07 08:45:16]

Done.

+
   // Deletes the favicons listed in |effects->affected_favicons| if they are
   // unsued. Fails silently (we don't care about favicons so much, so don't want
   // to stop everything if it fails). Fills |expired_favicons| with the set of
   // favicon urls that no longer have associated visits and were therefore
   // expired.
   void DeleteFaviconsIfPossible(DeleteEffects* effects);
 
   // Enum representing what type of action resulted in the history DB deletion.
   enum DeletionType {
     // User initiated the deletion from the History UI.
@@ skipping 71 matching lines @@
   // Used to generate runnable methods to do timers on this class. They will be
   // automatically canceled when this class is deleted.
   base::WeakPtrFactory<ExpireHistoryBackend> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExpireHistoryBackend);
 };
 
 }  // namespace history
 
 #endif  // COMPONENTS_HISTORY_CORE_BROWSER_EXPIRE_HISTORY_BACKEND_H_