[ios] Adds code to support the iOS Handoff feature.

ios/chrome/browser/pref_names.h

Index: ios/chrome/browser/pref_names.h
diff --git a/ios/chrome/browser/pref_names.h b/ios/chrome/browser/pref_names.h
index 5eca97af12a7777ee53ec00baa9d0662539ec0a2..feff827daa3de91f21a0bb52fca5fcdd91b438f3 100644
--- a/ios/chrome/browser/pref_names.h
+++ b/ios/chrome/browser/pref_names.h
@@ -5,8 +5,9 @@
 #ifndef IOS_CHROME_BROWSER_PREF_NAMES_H_
 #define IOS_CHROME_BROWSER_PREF_NAMES_H_
 
-// TODO(rohitrao): Remove this include once embedders are migrated to use the
-// new pref header.
+// TODO(crbug.com/663469): Remove these includes once embedders are migrated to
+// use the new pref header.
+#include "components/handoff/pref_names_ios.h"
 #include "ios/public/provider/chrome/browser/voice/voice_search_prefs.h"
 
 namespace prefs {
@@ -26,7 +27,6 @@ extern const char kEnableDoNotTrack[];
 extern const char kHttpServerProperties[];
 extern const char kIosBookmarkFolderDefault[];
 extern const char kIosBookmarkPromoAlreadySeen[];
-extern const char kIosHandoffToOtherDevices[];
 extern const char kIosPhysicalWebEnabled[];
 extern const char kLastSessionExitedCleanly[];
 extern const char kMetricsReportingWifiOnly[];