Fix Crash when closing incognito

WebSiteDataStore crashed during the destructing of WKHTTPCookieStore
The reason:
 WKHTTPCookieStore can't be deleted in IO Thread (undocumented behavior).
The solution:
 Make WKHTTPCookieStore instance in WKHTTPSystemCookieStore as weak, so
 it's not retained in WKHTTPSystemCookieStore and it's deleted/released
 when WebSiteDataStore is deleted.

Bug: 817460, 816879
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I15b384f41496df6d0af9c550b7b13e67a75d236b
Reviewed-on: https://chromium-review.googlesource.com/955547
Commit-Queue: Mohammad Refaat <mrefaat@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541973}

ios/web/net/cookies/wk_http_system_cookie_store.h

@@ -50,7 +50,10 @@ class API_AVAILABLE(ios(11.0)) WKHTTPSystemCookieStore
       net::SystemCookieStore::SystemCookieCallbackForCookies callback,
       NSArray<NSHTTPCookie*>* cookies);
 
-  WKHTTPCookieStore* cookie_store_;
+  // cookie_store_ must be deleted in the UI thread, So by making it weak
+  // WKHTTPSystemCookieStore will not retain the WKHTTPCookieStore instance, and
+  // it will be deleted with the owning WKWebSiteDataStore.
+  __weak WKHTTPCookieStore* cookie_store_;
 
   DISALLOW_COPY_AND_ASSIGN(WKHTTPSystemCookieStore);
 };

ios/web/net/cookies/wk_http_system_cookie_store.mm

@@ -63,6 +63,8 @@ WKHTTPSystemCookieStore::~WKHTTPSystemCookieStore() = default;
 void WKHTTPSystemCookieStore::GetCookiesForURLAsync(
     const GURL& url,
     SystemCookieCallbackForCookies callback) {
+  // This function shouldn't be called if cookie_store_ is deleted.
+  DCHECK(cookie_store_);
   __block SystemCookieCallbackForCookies shared_callback = std::move(callback);
   GURL block_url = url;
   web::WebThread::PostTask(
@@ -81,6 +83,8 @@ void WKHTTPSystemCookieStore::GetCookiesForURLAsync(
 
 void WKHTTPSystemCookieStore::GetAllCookiesAsync(
     SystemCookieCallbackForCookies callback) {
+  // This function shouldn't be called if cookie_store_ is deleted.
+  DCHECK(cookie_store_);
   __block SystemCookieCallbackForCookies shared_callback = std::move(callback);
   web::WebThread::PostTask(
       web::WebThread::UI, FROM_HERE, base::BindBlockArc(^{
@@ -93,6 +97,8 @@ void WKHTTPSystemCookieStore::GetAllCookiesAsync(
 
 void WKHTTPSystemCookieStore::DeleteCookieAsync(NSHTTPCookie* cookie,
                                                 SystemCookieCallback callback) {
+  // This function shouldn't be called if cookie_store_ is deleted.
+  DCHECK(cookie_store_);
   __block SystemCookieCallback shared_callback = std::move(callback);
   NSHTTPCookie* block_cookie = cookie;
   web::WebThread::PostTask(
@@ -111,6 +117,8 @@ void WKHTTPSystemCookieStore::SetCookieAsync(
     NSHTTPCookie* cookie,
     const base::Time* optional_creation_time,
     SystemCookieCallback callback) {
+  // cookies can't be set if cookie_store_ is deleted.
+  DCHECK(cookie_store_);
   __block SystemCookieCallback shared_callback = std::move(callback);
   NSHTTPCookie* block_cookie = cookie;
   base::Time cookie_time = base::Time::Now();