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

ios/web/web_state/navigation_callbacks_inttest.mm

Index: ios/web/web_state/navigation_callbacks_inttest.mm
diff --git a/ios/web/web_state/navigation_callbacks_inttest.mm b/ios/web/web_state/navigation_callbacks_inttest.mm
index 76e3b92fcd13bf3fa8ceddd66663539b1c5f5034..ec7867d5c4657691fd1f9a0eef85b9137e2424ca 100644
--- a/ios/web/web_state/navigation_callbacks_inttest.mm
+++ b/ios/web/web_state/navigation_callbacks_inttest.mm
@@ -509,9 +509,8 @@ TEST_F(NavigationCallbacksTest, MAYBE_UserInitiatedPostNavigation) {
 
   // Load request using POST HTTP method.
   web::NavigationManager::WebLoadParams params(url);
-  params.post_data.reset(
-      [[@"foo" dataUsingEncoding:NSUTF8StringEncoding] retain]);
-  params.extra_headers.reset([@{ @"Content-Type" : @"text/html" } retain]);
+  params.post_data.reset([@"foo" dataUsingEncoding:NSUTF8StringEncoding]);
+  params.extra_headers.reset(@{ @"Content-Type" : @"text/html" });
   LoadWithParams(params);
 }