DoomPartialEntry should not attempt to doom an already doomed entry.

net/http/http_cache.h

Index: net/http/http_cache.h
diff --git a/net/http/http_cache.h b/net/http/http_cache.h
index e420c7244204874988b4908149bf51a2bd8697a3..28ce090d4189c7780d07cbb50d914f4b30beec1c 100644
--- a/net/http/http_cache.h
+++ b/net/http/http_cache.h
@@ -341,7 +341,9 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory {
 
   // Dooms the entry selected by |key|. |trans| will be notified via its IO
   // callback if this method returns ERR_IO_PENDING. The entry can be
-  // currently in use or not.
+  // currently in use or not. If entry is in use and the invoking transaction
+  // is associated with this entry and this entry is already doomed, this API
+  // should not be invoked.
   int DoomEntry(const std::string& key, Transaction* trans);
 
   // Dooms the entry selected by |key|. |trans| will be notified via its IO