When displaying a single function's timeline, display all its variants
(colour-coded by kind) instead of just the ones with the same code-id.
This allows us to see all optimised versions of a function, as well as
changes between optimised and unoptimised.

Drive-by -- Do some rounding to get rendering pixel-perfect.

Change-Id: I385c83b39414ac5e59208b7a25b488d6a283e2b0

NOTRY=true

Change-Id: I385c83b39414ac5e59208b7a25b488d6a283e2b0
Reviewed-on: https://chromium-review.googlesource.com/455833
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43894}