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

components/handoff/handoff_manager.mm

Index: components/handoff/handoff_manager.mm
diff --git a/components/handoff/handoff_manager.mm b/components/handoff/handoff_manager.mm
index 23a557dce71ee0e47053d0c6841091ac9c108041..8434d7a1b1a626eaf0f463c836dde4df25c3a84c 100644
--- a/components/handoff/handoff_manager.mm
+++ b/components/handoff/handoff_manager.mm
@@ -6,11 +6,12 @@
 
 #include "base/logging.h"
 #include "base/mac/scoped_nsobject.h"
-#include "build/build_config.h"
 #include "net/base/mac/url_conversions.h"
 
 #if defined(OS_IOS)
 #include "base/ios/ios_util.h"
+#include "components/handoff/pref_names_ios.h"
+#include "components/pref_registry/pref_registry_syncable.h"  // nogncheck

[gab, 2016/11/08 21:26:22]

What does // nogncheck do?

[rohitrao (ping after 24h), 2016/11/08 23:39:33]

The pref_registry dependency is added conditionally, only on iOS, and the header
is similarly in an OS_IOS block.  But "gn check" doesn't understand how to
process #ifdefs, so when it runs on mac, it sees this include and complains
(correctly, on Mac) that the handoff target doesn't depend on pref_registry.

// nogncheck tells the checker to ignore this include.  It's generally used to
work around this kind of scenario.

 #endif
 
 #if defined(OS_MACOSX) && !defined(OS_IOS)
@@ -35,6 +36,14 @@
 
 @synthesize userActivity = _userActivity;
 
+#if defined(OS_IOS)
++ (void)registerBrowserStatePrefs:(user_prefs::PrefRegistrySyncable*)registry {
+  registry->RegisterBooleanPref(
+      prefs::kIosHandoffToOtherDevices, true,
+      user_prefs::PrefRegistrySyncable::SYNCABLE_PREF);
+}
+#endif
+
 - (instancetype)init {
   self = [super init];
   if (self) {
@@ -98,3 +107,11 @@
 }
 
 @end
+
+@implementation HandoffManager (TestingOnly)
+
+- (NSURL*)userActivityWebpageURL {
+  return self.userActivity.webpageURL;
+}
+
+@end