[ObjC ARC] Converts ios/web:earl_grey_test_support to ARC.

ios/web/public/test/earl_grey/js_test_util.mm

Index: ios/web/public/test/earl_grey/js_test_util.mm
diff --git a/ios/web/public/test/earl_grey/js_test_util.mm b/ios/web/public/test/earl_grey/js_test_util.mm
index b2bdcdf4ea3292d097a5ea2de3842595333e909b..f0a0bce830ecf8101faf16c984f4544f123f464d 100644
--- a/ios/web/public/test/earl_grey/js_test_util.mm
+++ b/ios/web/public/test/earl_grey/js_test_util.mm
@@ -12,6 +12,10 @@
 #import "ios/web/interstitials/web_interstitial_impl.h"
 #import "ios/web/public/web_state/js/crw_js_injection_receiver.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 using testing::kWaitForJSCompletionTimeout;
 using testing::WaitUntilConditionOrTimeout;
 
@@ -54,7 +58,7 @@ void WaitUntilWindowIdInjected(WebState* web_state) {
 
 id ExecuteJavaScript(WebState* web_state,
                      NSString* javascript,
-                     NSError** out_error) {
+                     NSError* __autoreleasing* out_error) {
   __block bool did_complete = false;
   __block id result = nil;
   CRWJSInjectionReceiver* receiver = web_state->GetJSInjectionReceiver();
@@ -72,9 +76,7 @@ id ExecuteJavaScript(WebState* web_state,
   });
   GREYAssert(suceeded, @"Script execution timed out");
 
-  if (out_error)
-    [*out_error autorelease];
-  return [result autorelease];
+  return result;
 }
 
 id ExecuteScriptOnInterstitial(WebState* web_state, NSString* script) {
@@ -91,7 +93,7 @@ id ExecuteScriptOnInterstitial(WebState* web_state, NSString* script) {
     return did_finish;
   });
   GREYAssert(suceeded, @"Script execution timed out");
-  return [script_result autorelease];
+  return script_result;
 }
 
 }  // namespace web