[ios] Fixed memory management in ExecuteScriptOnInterstitial.

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 f6d96f9e54c3689b28fd4aec89faa813611f3a59..b2bdcdf4ea3292d097a5ea2de3842595333e909b 100644
--- a/ios/web/public/test/earl_grey/js_test_util.mm
+++ b/ios/web/public/test/earl_grey/js_test_util.mm
@@ -84,14 +84,14 @@ id ExecuteScriptOnInterstitial(WebState* web_state, NSString* script) {
   __block id script_result = nil;
   __block bool did_finish = false;
   web::ExecuteScriptForTesting(interstitial, script, ^(id result, NSError*) {
-    script_result = [[result copy] autorelease];
+    script_result = [result copy];
     did_finish = true;
   });
   BOOL suceeded = WaitUntilConditionOrTimeout(kWaitForJSCompletionTimeout, ^{
     return did_finish;
   });
   GREYAssert(suceeded, @"Script execution timed out");
-  return script_result;
+  return [script_result autorelease];
 }
 
 }  // namespace web