[iOS] Add FakeSyncService and factory for testing

ios/public/test/test_chrome_browser_provider.mm

Index: ios/public/test/test_chrome_browser_provider.mm
diff --git a/ios/public/test/test_chrome_browser_provider.mm b/ios/public/test/test_chrome_browser_provider.mm
index afcf24ca596e548470fae0a27f21833056610942..df12eaad28e265a6395fa783ed8969016fd57c30 100644
--- a/ios/public/test/test_chrome_browser_provider.mm
+++ b/ios/public/test/test_chrome_browser_provider.mm
@@ -6,6 +6,7 @@
 
 #include "base/logging.h"
 #include "ios/public/test/fake_string_provider.h"
+#import "ios/public/test/test_keyed_service_provider.h"
 
 namespace {
 const char kUIScheme[] = "uischeme";
@@ -14,7 +15,8 @@ const char kUIScheme[] = "uischeme";
 namespace ios {
 
 TestChromeBrowserProvider::TestChromeBrowserProvider()
-    : string_provider_(new FakeStringProvider) {
+    : string_provider_(new FakeStringProvider),
+      test_keyed_service_provider_(new TestKeyedServiceProvider) {
 }
 
 TestChromeBrowserProvider::~TestChromeBrowserProvider() {
@@ -31,6 +33,10 @@ StringProvider* TestChromeBrowserProvider::GetStringProvider() {
   return string_provider_.get();
 }
 
+KeyedServiceProvider* TestChromeBrowserProvider::GetKeyedServiceProvider() {
+  return test_keyed_service_provider_.get();
+}
+
 const char* TestChromeBrowserProvider::GetChromeUIScheme() {
   return kUIScheme;
 }