Add MDP for TabRestorer.

components/sessions/core/tab_restore_service.h

Index: components/sessions/core/tab_restore_service.h
diff --git a/components/sessions/core/tab_restore_service.h b/components/sessions/core/tab_restore_service.h
index a851f813e575bd07c58300d79386a21e3e993ff9..b35fd57f16ad3cc6bd07947c88ab1b6bbdb8439c 100644
--- a/components/sessions/core/tab_restore_service.h
+++ b/components/sessions/core/tab_restore_service.h
@@ -69,6 +69,9 @@ class SESSIONS_EXPORT TabRestoreService : public KeyedService {
     // closed during this session.
     bool from_last_session = false;
 
+    // Estimates memory usage. By default returns 0.
+    virtual size_t EstimateMemoryUsage() const;
+
    protected:
     explicit Entry(Type type);
 
@@ -81,6 +84,8 @@ class SESSIONS_EXPORT TabRestoreService : public KeyedService {
     Tab();
     ~Tab() override;
 
+    size_t EstimateMemoryUsage() const override;
+
     // The navigations.
     std::vector<SerializedNavigationEntry> navigations;