Add bloaty_treemap.py, for visualizing bloaty data

There is so much more that could be done here (some ideas in TODO
comments), but this greatly streamlines the process for average
developers to navigate the code-size of skia executables.

Currently, I'm using a locally built copy of bloaty, but we should see
about using DEPS or adding a fetch-able package to eliminate even more
friction.

Change-Id: I92186c0370a1ab8d2c8edd73932547402c43612d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/428959
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed