Create a new disk_cache type, SHADER_CACHE.

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 e7fad5b9ffe8def36969239edca1ebe9a49d5541..2bbff55a663d128c7fa099e03ef09af14975a188 100644
--- a/net/disk_cache/backend_impl.cc
+++ b/net/disk_cache/backend_impl.cc
@@ -475,6 +475,8 @@ int BackendImpl::SyncInit() {
   if (cache_type() == net::APP_CACHE) {
     DCHECK(!new_eviction_);
     read_only_ = true;
+  } else if (cache_type() == net::SHADER_CACHE) {
+    DCHECK(!new_eviction_);
   }
 
   eviction_.Init(this);
@@ -919,9 +921,9 @@ LruData* BackendImpl::GetLruData() {
 }
 
 void BackendImpl::UpdateRank(EntryImpl* entry, bool modified) {
-  if (!read_only_) {
-    eviction_.UpdateRank(entry, modified);
-  }
+  if (read_only_ || (!modified && cache_type() == net::SHADER_CACHE))
+    return;
+  eviction_.UpdateRank(entry, modified);
 }
 
 void BackendImpl::RecoveredEntry(CacheRankingsBlock* rankings) {