Instant: Allow empty sets to be added to the cache.

chrome/common/instant_restricted_id_cache.h

Index: chrome/common/instant_restricted_id_cache.h
diff --git a/chrome/common/instant_restricted_id_cache.h b/chrome/common/instant_restricted_id_cache.h
index 66ae060a754be541c57df73a9230ad069c903ab8..1ca09ebffb77c116d9505273cf0ba2900440e330 100644
--- a/chrome/common/instant_restricted_id_cache.h
+++ b/chrome/common/instant_restricted_id_cache.h
@@ -68,6 +68,7 @@ class InstantRestrictedIDCache {
   FRIEND_TEST_ALL_PREFIXES(InstantRestrictedIDCacheTest, CrazyIDGeneration);
   FRIEND_TEST_ALL_PREFIXES(InstantRestrictedIDCacheTest, ManualIDGeneration);
   FRIEND_TEST_ALL_PREFIXES(InstantRestrictedIDCacheTest, MixIDGeneration);
+  FRIEND_TEST_ALL_PREFIXES(InstantRestrictedIDCacheTest, AddEmptySet);
 
   typedef base::MRUCache<InstantRestrictedID, T> CacheImpl;
 
@@ -92,9 +93,14 @@ InstantRestrictedIDCache<T>::~InstantRestrictedIDCache() {
 
 template <typename T>
 void InstantRestrictedIDCache<T>::AddItems(const ItemVector& items) {
-  if (items.size() == 0 || items.size() > cache_.max_size())
+  if (items.size() > cache_.max_size())
     return;

[brettw, 2013/03/25 22:26:52]

I'm wondering about this. If you add too many items, does this actually do what
we want? The current items will still be the old ones. It seems like you would
want the same behavior as you currently have in the "add an empty vector" case.

[sreeram, 2013/03/25 22:29:33]

Adding too many items would be an error situation, i.e., not supported. Changing
it to be the same as adding an empty set (which _is_ supported) would give the
wrong impression of stuff working, while in fact silently breaking things. I
don't mind changing the 'if' to a DCHECK(), if you prefer?

[brettw, 2013/03/25 22:34:04]

Yeah, I like the dcheck.

[sreeram, 2013/03/25 22:39:26]

Done.

 
+  if (items.empty()) {
+    last_add_start_ = cache_.rend();
+    return;
+  }
+
   for (size_t i = 0; i < items.size(); ++i) {
     InstantRestrictedID id = ++last_restricted_id_;
     cache_.Put(id, items[i]);
@@ -106,9 +112,14 @@ void InstantRestrictedIDCache<T>::AddItems(const ItemVector& items) {
 template <typename T>
 void InstantRestrictedIDCache<T>::AddItemsWithRestrictedID(
     const ItemIDVector& items) {
-  if (items.size() == 0 || items.size() > cache_.max_size())
+  if (items.size() > cache_.max_size())
     return;
 
+  if (items.empty()) {
+    last_add_start_ = cache_.rend();
+    return;
+  }
+
   std::set<InstantRestrictedID> ids_added;
   for (size_t i = 0; i < items.size(); ++i) {
     const ItemIDPair& item_id = items[i];