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

ios/chrome/test/BUILD.gn

Index: ios/chrome/test/BUILD.gn
diff --git a/ios/chrome/test/BUILD.gn b/ios/chrome/test/BUILD.gn
index 44ac22f58b65a0857655a95b1f8b729e5dfdf1c6..3ec9015b9d82f5153663f1de70fde346cd700d37 100644
--- a/ios/chrome/test/BUILD.gn
+++ b/ios/chrome/test/BUILD.gn
@@ -17,10 +17,9 @@ group("all_tests") {
 }
 
 source_set("test_support") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   testonly = true
   sources = [
-    "block_cleanup_test.h",
-    "block_cleanup_test.mm",
     "ios_chrome_scoped_testing_chrome_browser_provider.h",
     "ios_chrome_scoped_testing_chrome_browser_provider.mm",
     "ios_chrome_scoped_testing_chrome_browser_state_manager.cc",
@@ -34,6 +33,10 @@ source_set("test_support") {
     "testing_application_context.mm",
   ]
 
+  public_deps = [
+    ":block_cleanup_test",
+  ]
+
   deps = [
     "//base",
     "//base/test:test_support",
@@ -57,6 +60,21 @@ source_set("test_support") {
   ]
 }
 
+source_set("block_cleanup_test") {
+  # TODO(crbug.com/733237): Replace this comment with an explicit disable_arc config.
+  # The files in this target depend on non-ARC memeory management.
+  testonly = true
+  sources = [
+    "block_cleanup_test.h",
+    "block_cleanup_test.mm",
+  ]
+
+  deps = [
+    "//base",
+    "//testing/gtest",
+  ]
+}
+
 source_set("run_all_unittests") {
   testonly = true
   sources = [