Efficient chunk iterator
Efficient chunk iterator

The iterator over chunks now caches the nodes so it doesn't have to
descend from the root each iteration.

fuchsia-mirror/third_party-xi-editor,google/xi-editor,google/xi-editor,modelorganism/xi-editor,google/xi-editor,google/xi-editor,fuchsia-mirror/third_party-xi-editor,fuchsia-mirror/third_party-xi-editor,modelorganism/xi-editor,fuchsia-mirror/third_party-xi-editor,modelorganism/xi-editor