Do not DCHECK on SimpleCache deletion-while-closing.

net/disk_cache/simple/simple_index_file.cc

Index: net/disk_cache/simple/simple_index_file.cc
diff --git a/net/disk_cache/simple/simple_index_file.cc b/net/disk_cache/simple/simple_index_file.cc
index c6a29a28333d99d2617adfa7f26911760c632177..91dc3b7d77a35edb190f70f03f0fb7eb1bb0c149 100644
--- a/net/disk_cache/simple/simple_index_file.cc
+++ b/net/disk_cache/simple/simple_index_file.cc
@@ -71,7 +71,7 @@ void UmaRecordIndexInitMethod(IndexInitMethod method,
 bool WritePickleFile(Pickle* pickle, const base::FilePath& file_name) {
   File file(
       file_name,
-      File::FLAG_CREATE_ALWAYS | File::FLAG_WRITE | File::FLAG_SHARE_DELETE);
+      File::FLAG_CREATE | File::FLAG_WRITE | File::FLAG_SHARE_DELETE);

[gavinp, 2014/10/30 18:59:20]

This change is good to do while we are here: if multiple serializations of the
same index are overlapping, this causes the second one to abort. This may
actually enhance the entry not found problem you describe in the underlying
issue; esp on Linux, so expect some changes here.

   if (!file.IsValid())
     return false;
 
@@ -222,8 +222,8 @@ void SimpleIndexFile::SyncWriteToDisk(net::CacheType cache_type,
   }
 
   // Atomically rename the temporary index file to become the real one.
-  bool result = base::ReplaceFile(temp_index_filename, index_filename, NULL);
-  DCHECK(result);
+  if (!base::ReplaceFile(temp_index_filename, index_filename, NULL))
+    return;
 

[jkarlin, 2014/10/30 19:19:24]

Would be better to replace DCHECK(result) with DCHECK(result || shutting_down)
so that other writes are still checked.

[gavinp, 2014/10/31 13:55:54]

That data isn't easily available here; it would require some plumbing through.
I've added a TODO and a discussion of the reasoning.

   if (app_on_background) {
     SIMPLE_CACHE_UMA(TIMES,