Update the build instructions to be consistent.

We have lots of inconsistencies between the different platforms in the
public instructions, and between the public instructions and the internal
instructions.

This CL (along with an internal one) should clean everything up.

[email protected], [email protected]
NOTRY=true

Review-Url: https://codereview.chromium.org/2526563003
Cr-Commit-Position: refs/heads/master@{#435138}
20 files changed