Adding mediator for Sign-in promo

ios/chrome/browser/ui/authentication/BUILD.gn

Index: ios/chrome/browser/ui/authentication/BUILD.gn
diff --git a/ios/chrome/browser/ui/authentication/BUILD.gn b/ios/chrome/browser/ui/authentication/BUILD.gn
index b41e78c1e9871413bf087673b62c20dc1fb3f29f..2550592c91ddc04c384f37ae0fa6551a2e78b9f7 100644
--- a/ios/chrome/browser/ui/authentication/BUILD.gn
+++ b/ios/chrome/browser/ui/authentication/BUILD.gn
@@ -87,13 +87,22 @@ source_set("authentication_arc") {
     "account_control_item.mm",
     "resized_avatar_cache.h",
     "resized_avatar_cache.mm",
+    "signin_promo_item.h",

[msarda, 2017/03/22 12:18:38]

Note that authentication_arc depends on the
//ios/public/provider/chrome/browser/signin which includes ChromeIdentity and
ChromeIdentityService etc. If the intent for this SigninPromoCell is never
depend on the model, then I suggest we move them to a new and different target -
maybe something like 'signin_promo_cell' that does not depend on
//ios/public/provider/chrome/browser/signin 

[lpromero, 2017/03/22 16:18:49]

Can you create a authentication_ui target in this file that will contain only
the UI layer (items, cells, views, view controllers)?
This is the target that Showcase should depend on for example.

[jlebel, 2017/03/24 20:59:08]

If I create authentication_ui target with all views and view controllers, I will
have to include //ios/public/provider/chrome/browser/signin since the rest do
mix UI and model API.
I need to put only my item, cell and view to be able to remove
//ios/public/provider/chrome/browser/signin

I don't use Showcase, I use "Cell Catalog".

[lpromero, 2017/03/27 13:14:46]

Right, I meant that the authentication_ui will ultimately contain these. In the
meantime, they contain as much UI as possible, which does not include VC yet, as
it has not been decoupled.

+    "signin_promo_item.mm",
+    "signin_promo_view.h",
+    "signin_promo_view.mm",
+    "signin_promo_view_mediator.h",
+    "signin_promo_view_mediator.mm",
   ]
   deps = [
+    "//base",
+    "//ios/chrome/app/strings",
     "//ios/chrome/browser/ui",
     "//ios/chrome/browser/ui/collection_view/cells",
     "//ios/chrome/browser/ui/colors",
     "//ios/public/provider/chrome/browser",
     "//ios/public/provider/chrome/browser/signin",
+    "//ui/base",
   ]
   libs = [
     "CoreGraphics.framework",
@@ -110,6 +119,8 @@ source_set("unit_tests") {
     "authentication_flow_unittest.mm",
     "re_signin_infobar_delegate_unittest.mm",
     "signed_in_accounts_view_controller_unittest.mm",
+    "signin_promo_item_unittest.mm",
+    "signin_promo_view_mediator_unittest.mm",
   ]
   deps = [
     ":authentication",