cc: Implement geometry-based tile eviction

cc/resources/eviction_tile_priority_queue.cc

Index: cc/resources/eviction_tile_priority_queue.cc
diff --git a/cc/resources/eviction_tile_priority_queue.cc b/cc/resources/eviction_tile_priority_queue.cc
index 4d6698745897caaa320a0584b2e8a4bae120ccac..5fba87c74dd9fcf9327ca1e23e0b006a400f8873 100644
--- a/cc/resources/eviction_tile_priority_queue.cc
+++ b/cc/resources/eviction_tile_priority_queue.cc
@@ -208,6 +208,16 @@ EvictionTilePriorityQueue::PairedTilingSetQueue::NextTileIteratorTree(
   const TilePriority& pending_priority =
       pending_tile->priority_for_tree_priority(tree_priority);
 
+  if (active_priority.priority_bin == pending_priority.priority_bin) {

[vmpstr, 2014/12/09 02:10:58]

While here, can you add a couple more comments in this functions:

at line 202, something like:
// If tiles are the same, it doesn't matter which tree we return.

before this block, something like:
// If the bins are the same and activation differs, then return the tree of the
tile not required for activaiton.

and below this block:
// Return tile with a lower priority.

[USE eero AT chromium.org, 2014/12/09 18:44:14]

Done.

+    if (active_tile->required_for_activation()) {
+      if (!pending_tile->required_for_activation())

[vmpstr, 2014/12/09 02:10:58]

I think this can be a bit simpler:

if (active_priority.priority_bin == pending_priority.priority_bin &&
    active_tile->required_for_activation() !=    
        pending_tile_required_for_activation()) {
 return active_tile->required_for_activation()
            ? PENDING_TREE : ACTIVE_TREE;
}

That works, right?

[USE eero AT chromium.org, 2014/12/09 18:44:14]

Yes. Done.

+        return PENDING_TREE;
+    } else {
+      if (pending_tile->required_for_activation())
+        return ACTIVE_TREE;
+    }
+  }
+
   if (pending_priority.IsHigherPriorityThan(active_priority))
     return ACTIVE_TREE;
   return PENDING_TREE;