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

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

Review-Url: https://codereview.chromium.org/2677193003
Cr-Commit-Position: refs/heads/master@{#450732}
diff --git a/ios/chrome/browser/ui/webui/BUILD.gn b/ios/chrome/browser/ui/webui/BUILD.gn
index df43c20d..2838f39 100644
--- a/ios/chrome/browser/ui/webui/BUILD.gn
+++ b/ios/chrome/browser/ui/webui/BUILD.gn
@@ -83,6 +83,7 @@
 }
 
 source_set("eg_tests") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
     "web_ui_egtest.mm",