This makes sure we use ninja everywhere if not stated
otherwise explicitly.

BUG=chromium:474921

Review-Url: https://codereview.chromium.org/2078393002
Cr-Commit-Position: refs/heads/master@{#37095}

This prepares for pulling chromium's build as dependency for
gn. After this, the files in build and gypfiles need to stay
in sync until chromium is updated.

BUG=chromium:474921
LOG=n

Review-Url: https://codereview.chromium.org/1848553003
Cr-Commit-Position: refs/heads/master@{#35898}

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}