[ObjC ARC] Converts ios/chrome/browser/ui/collection_view:collection_view to ARC.

ios/chrome/browser/ui/collection_view/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("collection_view") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "collection_view_controller.h",
     "collection_view_controller.mm",
     "collection_view_model.h",
     "collection_view_model.mm",
   ]
   deps = [
     "//base",
     "//ios/chrome/browser/ui/material_components",
   ]
   public_deps = [
     "//ios/chrome/browser/ui/collection_view/cells",
     "//ios/third_party/material_components_ios",
   ]
 }
 
 source_set("test_support") {
   testonly = true
   sources = [
     "collection_view_controller_test.h",

[lpromero, 2017/03/09 16:23:02]

Is this on the list to be migrated too?

     "collection_view_controller_test.mm",
   ]
   deps = [
     ":collection_view",
     "//base",
     "//ios/chrome/browser/ui/collection_view/cells",
     "//ios/chrome/test:test_support",
     "//ios/third_party/material_components_ios",
     "//testing/gtest",
     "//ui/base",
@@ skipping 10 matching lines @@
   deps = [
     ":collection_view",
     "//base",
     "//ios/chrome/browser/ui/collection_view/cells",
     "//ios/chrome/test:test_support",
     "//ios/chrome/test/base",
     "//ios/third_party/material_components_ios",
     "//testing/gtest",
   ]
 }