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

ios/chrome/browser/device_sharing/BUILD.gn

+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+source_set("device_sharing") {
+  sources = [
+    "device_sharing_manager.h",
+    "device_sharing_manager.mm",
+    "handoff_manager.h",
+    "handoff_manager.mm",
+  ]
+  deps = [
+    "//base",
+    "//components/handoff",
+    "//components/pref_registry",
+    "//components/prefs",
+    "//ios/chrome/browser",
+    "//ios/chrome/browser/browser_state",
+    "//ios/chrome/browser/prefs",
+    "//net",
+    "//url",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "device_sharing_manager_unittest.mm",
+  ]
+  deps = [
+    ":device_sharing",
+    "//base",
+    "//components/sync_preferences:test_support",
+    "//ios/chrome/browser",
+    "//ios/chrome/browser/browser_state:test_support",
+    "//ios/web:test_support",
+    "//testing/gtest",
+    "//third_party/ocmock",
+    "//url",
+  ]
+}