chrome: Add out-of-line copy ctors for complex classes.

chrome/browser/memory/tab_stats.h

Index: chrome/browser/memory/tab_stats.h
diff --git a/chrome/browser/memory/tab_stats.h b/chrome/browser/memory/tab_stats.h
index 8c6b48a35793aa566ea356d424c9809976b88325..c68f6d0661d92cebd0e375cf8e958c4e2cb0cada 100644
--- a/chrome/browser/memory/tab_stats.h
+++ b/chrome/browser/memory/tab_stats.h
@@ -22,6 +22,7 @@ namespace memory {
 
 struct TabStats {
   TabStats();
+  TabStats(const TabStats& other);
   ~TabStats();
   bool is_app;            // Browser window is an app.
   bool is_internal_page;  // Internal page, such as NTP or Settings.