Add MDP for TabRestorer.

components/sessions/core/tab_restore_service.cc

Index: components/sessions/core/tab_restore_service.cc
diff --git a/components/sessions/core/tab_restore_service.cc b/components/sessions/core/tab_restore_service.cc
index 8bf31952e703bbb88e0ab30d3ff8cd1ae0bbb61a..882eb5acf533b8465c57be6c26cbae5c2040a671 100644
--- a/components/sessions/core/tab_restore_service.cc
+++ b/components/sessions/core/tab_restore_service.cc
@@ -4,6 +4,8 @@
 
 #include "components/sessions/core/tab_restore_service.h"
 
+#include "base/trace_event/estimate_memory_usage.h"
+
 namespace sessions {
 
 // TimeFactory-----------------------------------------------------------------
@@ -18,9 +20,21 @@ static SessionID::id_type next_entry_id = 1;
 TabRestoreService::Entry::~Entry() = default;
 TabRestoreService::Entry::Entry(Type type) : id(next_entry_id++), type(type) {}
 
+size_t TabRestoreService::Entry::EstimateMemoryUsage() const {
+  return 0;
+}
+
 TabRestoreService::Tab::Tab() : Entry(TAB) {}
 TabRestoreService::Tab::~Tab() = default;
 
+size_t TabRestoreService::Tab::EstimateMemoryUsage() const {
+  using base::trace_event::EstimateMemoryUsage;
+  return
+      EstimateMemoryUsage(navigations) +
+      EstimateMemoryUsage(extension_app_id) +
+      EstimateMemoryUsage(user_agent_override);
+}
+
 TabRestoreService::Window::Window() : Entry(WINDOW) {}
 TabRestoreService::Window::~Window() = default;