This ports some code from chromium for using the bundled
toolchain.

BUG=chromium:548586
LOG=n

Review URL: https://codereview.chromium.org/1237803003

Cr-Commit-Position: refs/heads/master@{#31706}

This runs the landmines script as a gclient hook. It can
as such be used to clobber local checkouts when hooks are
run locally.

It is a softer version than chromium's landmines script, as
it only deletes directories in the output directory due
to compatibility with MSVS which has "build" hardcoded as
output directory in several places.

BUG=chromium:403263
LOG=n

Review URL: https://codereview.chromium.org/955463002

Cr-Commit-Position: refs/heads/master@{#26831}