Use UpdateDistributionForFlatTreeTraversal in selector_query

This is a follow-up CL for http://crrev.com/c/1025155.
SelectorQuery updates distribution only for traversing a flat tree.

Bug: 776656
Change-Id: I07312acc73abdc593a7ef81f04761bacc3d978d0
Reviewed-on: https://chromium-review.googlesource.com/1029560
Reviewed-by: Takayoshi Kochi <kochi@chromium.org>
Commit-Queue: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553938}
1 file changed