[tools] Add a tool to show potentially missing source deps.
[tools] Add a tool to show potentially missing source deps.

NOTRY=true

Review URL: https://codereview.chromium.org/1208573002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#29318}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh