Previously, when given a log with few ticks, the timeline would lump
them all into one or two buckets. This patch allows ticks to be assigned
to buckets more sparsely.

This patch also fixes a bug where there was a gap on the right side of
the timeline, which also caused the function tick marks to be slightly
misaligned. This was more noticable with fewer buckets.

Bug: v8:6240
Change-Id: Ib7353c0420caec8591590815271d329ea1a030fb
Reviewed-on: https://chromium-review.googlesource.com/1174440
Commit-Queue: Bret Sepulveda <bsep@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55125}