[ObjC ARC] Converts ios/web/shell/test to ARC.

ios/web/shell/test/earl_grey/shell_matchers.mm

Index: ios/web/shell/test/earl_grey/shell_matchers.mm
diff --git a/ios/web/shell/test/earl_grey/shell_matchers.mm b/ios/web/shell/test/earl_grey/shell_matchers.mm
index 5e71d586fcaf04b655d23df432dffb640bcbae79..ae4d07b2573a0fd3250f1bb5136fd714466b2025 100644
--- a/ios/web/shell/test/earl_grey/shell_matchers.mm
+++ b/ios/web/shell/test/earl_grey/shell_matchers.mm
@@ -13,6 +13,10 @@
 #import "ios/web/shell/test/app/web_shell_test_util.h"
 #import "ios/web/shell/view_controller.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 
 id<GREYMatcher> webViewContainingText(const std::string& text) {
@@ -54,9 +58,8 @@ id<GREYMatcher> addressFieldText(std::string text) {
     [description appendText:base::SysUTF8ToNSString(text)];
   };
 
-  return [[[GREYElementMatcherBlock alloc] initWithMatchesBlock:matches
-                                               descriptionBlock:describe]
-      autorelease];
+  return [[GREYElementMatcherBlock alloc] initWithMatchesBlock:matches
+                                              descriptionBlock:describe];
 }
 
 id<GREYMatcher> backButton() {