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

components/handoff/BUILD.gn

Index: components/handoff/BUILD.gn
diff --git a/components/handoff/BUILD.gn b/components/handoff/BUILD.gn
index 1eea43c1088ca952ee950d669abda11fe4cd882e..e669fa88c11d3856ebbe8e04bb154b2d81ad7a69 100644
--- a/components/handoff/BUILD.gn
+++ b/components/handoff/BUILD.gn
@@ -5,14 +5,10 @@
 source_set("handoff") {
   if (is_mac || is_ios) {
     sources = [
-      "handoff_utility.h",
-      "handoff_utility.mm",
-    ]
-  }
-  if (is_mac) {
-    sources += [
       "handoff_manager.h",
       "handoff_manager.mm",
+      "handoff_utility.h",
+      "handoff_utility.mm",
     ]
     deps = [
       "//base",
@@ -20,4 +16,11 @@ source_set("handoff") {
       "//url",
     ]
   }
+  if (is_ios) {
+    sources += [
+      "pref_names_ios.cc",
+      "pref_names_ios.h",
+    ]
+    deps += [ "//components/pref_registry" ]
+  }
 }