[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..05ac22100f48e27398188dea6e5bc049490abcc8 100644
--- a/components/history/core/browser/history_types.cc
+++ b/components/history/core/browser/history_types.cc
@@ -299,6 +299,14 @@ FaviconBitmapIDSize::FaviconBitmapIDSize() {}
 
 FaviconBitmapIDSize::~FaviconBitmapIDSize() {}
 
+// FaviconURLs ----------------------------------------------------------------
+
+FaviconURLs::FaviconURLs() {}
+
+FaviconURLs::FaviconURLs(const FaviconURLs& other) = default;
+
+FaviconURLs::~FaviconURLs() {}
+
 // FaviconBitmap --------------------------------------------------------------
 
 FaviconBitmap::FaviconBitmap() {}