Add python-yaml to install-build-deps
Add python-yaml to install-build-deps

We'd like to use the |yaml| Python package to parse yaml files.

This CL is a cherry-pick of chromium@df3a88fdd315c9fe3d7a65850d919e976dd2d6b2

R=eseidel@chromium.org, eseidel@google.com

Review URL: https://codereview.chromium.org/1220823005.

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