Add ninja console pool support to GN

Allow GN actions to specify "console = true", which will translate into
a "pool = console" setting in the generated ninja files. The console
pool allows a ninja target to have unbuffered io, access to standard
input, and is limited to one target at a time.

R=brettw@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1358803002

Cr-Commit-Position: refs/heads/master@{#350321}
9 files changed