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

ios/chrome/browser/device_sharing/handoff_manager.mm

+// Copyright 2014 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.
+
+#import "ios/chrome/browser/device_sharing/handoff_manager.h"
+
+#include "base/logging.h"
+#include "base/mac/objc_property_releaser.h"
+#import "base/mac/scoped_nsobject.h"
+#include "components/handoff/handoff_utility.h"
+#include "components/pref_registry/pref_registry_syncable.h"
+#include "ios/chrome/browser/pref_names.h"
+#import "net/base/mac/url_conversions.h"
+#include "url/gurl.h"
+
+@interface HandoffManager () {
+  base::mac::ObjCPropertyReleaser _propertyReleaser_HandoffManager;
+  GURL _activeURL;

[erikchen, 2016/11/07 22:02:08]

I think you should remove this line and add an explicit synthesize.

[rohitrao (ping after 24h), 2016/11/08 02:19:42]

No longer relevant, this file has been deleted from the CL.

+}
+
+// The active URL is exposed via the Handoff API. It is defined as the URL of
+// the most recently accessed tab.
+@property(nonatomic, assign) const GURL& activeURL;
+
+// The active user activity.
+@property(nonatomic, retain) NSUserActivity* userActivity;
+
+// Whether the URL of the current tab should be exposed for Handoff.
+- (BOOL)shouldUseActiveURL;
+
+// Updates the active NSUserActivity.
+- (void)updateUserActivity;
+
+@end
+
+@implementation HandoffManager
+
+@synthesize userActivity = _userActivity;
+
++ (void)registerBrowserStatePrefs:(user_prefs::PrefRegistrySyncable*)registry {
+  registry->RegisterBooleanPref(
+      prefs::kIosHandoffToOtherDevices, true,
+      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+}
+
+- (instancetype)init {
+  self = [super init];
+  if (self) {
+    _propertyReleaser_HandoffManager.Init(self, [HandoffManager class]);
+  }
+  return self;
+}
+
+- (void)updateActiveURL:(const GURL&)url {
+  self.activeURL = url;
+  [self updateUserActivity];
+}
+
+- (void)setActiveURL:(const GURL&)url {
+  _activeURL = url;
+}
+
+- (const GURL&)activeURL {
+  return _activeURL;
+}
+
+- (BOOL)shouldUseActiveURL {
+  return self.activeURL.SchemeIsHTTPOrHTTPS();
+}
+
+- (void)updateUserActivity {
+  // Clear the user activity.
+  if (![self shouldUseActiveURL]) {
+    [self.userActivity invalidate];
+    self.userActivity = nil;
+    return;
+  }
+
+  // No change to the user activity.
+  const GURL userActivityURL(net::GURLWithNSURL(self.userActivity.webpageURL));
+  if (userActivityURL == self.activeURL)
+    return;
+
+  // Invalidate the old user activity and make a new one.
+  [self.userActivity invalidate];
+  self.userActivity =
+      base::scoped_nsobject<NSUserActivity>([[NSUserActivity alloc]
+          initWithActivityType:handoff::kChromeHandoffActivityType]);
+  self.userActivity.webpageURL = net::NSURLWithGURL(self.activeURL);
+  self.userActivity.userInfo = @{handoff::kOriginKey : handoff::kOriginiOS};
+  [self.userActivity becomeCurrent];
+}
+
+@end
+
+@implementation HandoffManager (TestingOnly)
+
+- (NSURL*)userActivityWebpageURL {
+  return self.userActivity.webpageURL;
+}
+
+@end