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

Automatically generated ARCMigrate commit
Notable issues:None
BUG=624363
TEST=None

Review-Url: https://codereview.chromium.org/2802703002
Cr-Commit-Position: refs/heads/master@{#462829}

ios/chrome/browser/ui/BUILD.gn

@@ -349,6 +349,7 @@ source_set("ui_internal") {
 }
 
 source_set("test_support") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "browser_view_controller_testing.h",

ios/chrome/browser/ui/browser_view_controller_testing.mm

@@ -7,6 +7,10 @@
 #import "ios/chrome/browser/ui/toolbar/web_toolbar_controller.h"
 #import "ios/chrome/browser/ui/toolbar/web_toolbar_controller_private.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @interface BrowserViewController (Private)
 
 - (WebToolbarController*)toolbarController;