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Also makes the filter bar thinner.

Screenshots: https://imgur.com/a/CClua

First round of reviews here: https://codereview.chromium.org/2105023004

BUG=606897
TEST=open network panel, padding for selected filter (XHR, JS, CSS)
should be even (see screenshots)

Review-Url: https://codereview.chromium.org/2150503002
Cr-Commit-Position: refs/heads/master@{#405154}