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This makes it easier to visually associate frames to their process.
Also make the nodes slightly bigger and turn the stroke around them
black for better contrast, as the colors are fairly muted.

Change-Id: I80b9a817bbed852aa558fbfcacc6d28690f477b8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1586228
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654865}