Skip updating rank in OnExternalCacheHit if cache is uninitialized or disabled.

net/disk_cache/backend_impl.cc

Index: net/disk_cache/backend_impl.cc
diff --git a/net/disk_cache/backend_impl.cc b/net/disk_cache/backend_impl.cc
index deacdd3c7eb4e23857e947ee845ccc3452458ec3..520be91ca2814f789bca3a9e4cc93b9ae782d44c 100644
--- a/net/disk_cache/backend_impl.cc
+++ b/net/disk_cache/backend_impl.cc
@@ -683,6 +683,9 @@ void BackendImpl::SyncEndEnumeration(void* iter) {
 }
 
 void BackendImpl::SyncOnExternalCacheHit(const std::string& key) {
+  if (disabled_)
+    return;
+
   uint32 hash = Hash(key);
   bool error;
   EntryImpl* cache_entry = MatchEntry(key, hash, false, Addr(), &error);