AppCache: fix a browser crashing bug that can happen during updates.

content/browser/appcache/appcache_update_job.cc

Index: content/browser/appcache/appcache_update_job.cc
diff --git a/content/browser/appcache/appcache_update_job.cc b/content/browser/appcache/appcache_update_job.cc
index e0c237261388f379a8370688a0acb8849bf1eb63..708f4439dfe2e4cd9aba9486227e67a59c910b1a 100644
--- a/content/browser/appcache/appcache_update_job.cc
+++ b/content/browser/appcache/appcache_update_job.cc
@@ -427,6 +427,9 @@ void AppCacheUpdateJob::StartUpdate(AppCacheHost* host,
     DCHECK(!new_master_resource.has_ref());
     DCHECK(new_master_resource.GetOrigin() == manifest_url_.GetOrigin());
 
+    if (ContainsKey(failed_master_entries_, new_master_resource))
+      return;

[gzobqq, 2015/11/20 06:10:54]

Do we care about lack of host notification?

[michaeln, 2015/11/20 20:38:55]

we care more about the crash

for this to happen, the master resource load must succeed a moment earlier and
then fail to load a moment later. this seems like a small corner case. i think
trading minor correctness errors (visible events) in that case for robustness is
a reasonable trade.

[michaeln, 2015/11/20 21:19:15]

If we were to care... looks like the sequence of expected events should be:
CHECKING, DOWNLOADING, ERROR and AssociateNoCache(GURL())?

+
     // Cannot add more to this update if already terminating.
     if (IsTerminating()) {
       group_->QueueUpdate(host, new_master_resource);
@@ -864,6 +867,8 @@ void AppCacheUpdateJob::HandleMasterEntryFetchCompleted(
     }
     hosts.clear();
 
+    failed_master_entries_.insert(url);
+
     const char* kFormatString = "Manifest fetch failed (%d) %s";
     std::string message = FormatUrlErrorMessage(
         kFormatString, request->url(), fetcher->result(), response_code);