Ensure depot_tools/ninja is used
Ensure depot_tools/ninja is used

BUG=skia:5742

Change-Id: Ica2f360528319036011147d0c584d8708d8ab909
Reviewed-on: https://skia-review.googlesource.com/2346
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot