Annotates functions returning retained objects.

ios/web/web_state/ui/crw_web_controller_unittest.mm

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "ios/web/web_state/ui/crw_web_controller.h"
 
 #import <WebKit/WebKit.h>
 
 #include <utility>
 
@@ skipping 298 matching lines @@
 
   // The value for web view OCMock objects to expect for |-setFrame:|.
   CGRect ExpectedWebViewFrame() const {
     CGSize containerViewSize = [UIScreen mainScreen].bounds.size;
     containerViewSize.height -=
         CGRectGetHeight([UIApplication sharedApplication].statusBarFrame);
     return {CGPointZero, containerViewSize};
   }
 
   // Creates WebView mock.
-  UIView* CreateMockWebView() {
+  UIView* CreateMockWebView() NS_RETURNS_RETAINED {
     id result = [[OCMockObject mockForClass:[WKWebView class]] retain];
 
     if (base::ios::IsRunningOnIOS10OrLater()) {
       [[result stub] serverTrust];
     } else {
       [[result stub] certificateChain];
     }
 
     [[result stub] backForwardList];
     [[[result stub] andReturn:[NSURL URLWithString:kTestURLString]] URL];
@@ skipping 675 matching lines @@
 
   [web_controller() setDelegate:delegate];
   web::SimulateWKWebViewCrash(webView_);
 
   EXPECT_OCMOCK_VERIFY(delegate);
   EXPECT_FALSE([web_controller() isViewAlive]);
   [web_controller() setDelegate:nil];
 };
 
 }  // namespace