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

components/history/core/browser/history_types.cc

Index: components/history/core/browser/history_types.cc
diff --git a/components/history/core/browser/history_types.cc b/components/history/core/browser/history_types.cc
index 1624e636b2ad60b4d51938a33995f34272b90470..7365619b0a8ba306736bdbd8df5905dc7f19f17e 100644
--- a/components/history/core/browser/history_types.cc
+++ b/components/history/core/browser/history_types.cc
@@ -299,6 +299,15 @@ FaviconBitmapIDSize::FaviconBitmapIDSize() {}
 
 FaviconBitmapIDSize::~FaviconBitmapIDSize() {}
 
+// IconMappingsForExpiry ------------------------------------------------------
+
+IconMappingsForExpiry::IconMappingsForExpiry() {}
+
+IconMappingsForExpiry::IconMappingsForExpiry(
+    const IconMappingsForExpiry& other) = default;
+
+IconMappingsForExpiry::~IconMappingsForExpiry() {}
+
 // FaviconBitmap --------------------------------------------------------------
 
 FaviconBitmap::FaviconBitmap() {}