Increase shards for slow tests of win10_chromium_x64_rel_ng builder

I'd like to increase shards that has more than 20 mins execution time in win10_chromium_x64_rel_ng builder.
Slow tests are detected from below query
http://shortn/_39HQP6rTpb

AFAIK, win10_chromium_x64_rel_ng test does not have large per shard overhead.
And current win10 capacity seems to able to handle this.
http://shortn/_caTg5Sxv0F

Bug: 868114
Change-Id: Ib0dbeefac8e7fe12ea3ef7fd7ca49c1de4f34598
Reviewed-on: https://chromium-review.googlesource.com/c/1391038
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621783}
2 files changed