Add CSDataSource in showcase

ios/showcase/content_suggestions/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("content_suggestions") {
   sources = [
     "sc_content_suggestions_coordinator.h",
     "sc_content_suggestions_coordinator.mm",
+    "sc_content_suggestions_data_source.h",
+    "sc_content_suggestions_data_source.mm",
   ]
   deps = [
     "//base",
+    "//components/strings",
+    "//ios/chrome/app/strings",
     "//ios/chrome/browser/ui/content_suggestions",
+    "//ios/chrome/browser/ui/content_suggestions/identifier",
     "//ios/showcase/common",
+    "//ui/base",
+    "//ui/gfx",
+    "//url",

[lpromero, 2017/03/24 12:10:17]

Idem, only NSString should crossover. We need to keep ContentSuggestion out of
the UI layer and create intermediary objects. The mediator can do the
translation.

[gambard, 2017/03/24 15:12:49]

So, based on your doc, should I keep it? :)

[lpromero, 2017/03/24 15:22:54]

As of today, I'd say no, as people pushed back before I started the doc. So I
advise waiting a couple days so we get consensus.

   ]
   libs = [ "UIKit.framework" ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("eg_tests") {
   testonly = true
   sources = [
     "sc_content_suggestions_egtest.mm",
   ]
   deps = [
+    "//components/strings",
+    "//ios/chrome/app/strings",
+    "//ios/chrome/test/earl_grey:test_support",
     "//ios/showcase/test",
     "//ios/third_party/earl_grey",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }