Annotates functions returning retained objects.

ios/web/test/wk_web_view_crash_utils.mm

Index: ios/web/test/wk_web_view_crash_utils.mm
diff --git a/ios/web/test/wk_web_view_crash_utils.mm b/ios/web/test/wk_web_view_crash_utils.mm
index 936dc3064c23d1fe747ef3e2e8ded6048dfe9779..a3f6fa28cf4fff490d36bf3bc765a9b5298d3327 100644
--- a/ios/web/test/wk_web_view_crash_utils.mm
+++ b/ios/web/test/wk_web_view_crash_utils.mm
@@ -20,7 +20,7 @@ namespace {
 // Returns an OCMocked WKWebView whose |evaluateJavaScript:stringResultHandler:|
 // method has been mocked to execute |block| instead. |block| cannot be nil.
 WKWebView* CreateMockWKWebViewWithStubbedJSEvalFunction(
-    void (^block)(NSInvocation*)) {
+    void (^block)(NSInvocation*)) NS_RETURNS_RETAINED {
   DCHECK(block);
   web::TestBrowserState browser_state;
   base::scoped_nsobject<WKWebView> webView(
@@ -46,7 +46,7 @@ void SimulateWKWebViewCrash(WKWebView* webView) {
   [webView performSelector:@selector(_processDidExit)];
 }
 
-WKWebView* CreateTerminatedWKWebView() {
+WKWebView* CreateTerminatedWKWebView() NS_RETURNS_RETAINED {
   id fail = ^void(NSInvocation* invocation) {
       // Always fails with WKErrorWebContentProcessTerminated error.
       NSError* error =
@@ -61,7 +61,7 @@ WKWebView* CreateTerminatedWKWebView() {
   return CreateMockWKWebViewWithStubbedJSEvalFunction(fail);
 }
 
-WKWebView* CreateHealthyWKWebView() {
+WKWebView* CreateHealthyWKWebView() NS_RETURNS_RETAINED {
   id succeed = ^void(NSInvocation* invocation) {
       void (^completionHandler)(id, NSError*) =
           [invocation getArgumentAtIndexAsObject:3];