Roll src/third_party/depot_tools a0b8c5dcf189..9212599f6aac (3 commits)

https://chromium.googlesource.com/chromium/tools/depot_tools.git/+log/a0b8c5dcf189..9212599f6aac

git log a0b8c5dcf189..9212599f6aac --date=short --first-parent --format='%ad %ae %s'
2019-12-04 yiwzhang@google.com [recipes] replace the variable ${platform} with resolved-platform in test output
2019-12-04 ehmaldonado@chromium.org Revert "[bot_update] Also bootstrap in the case that there are 0 pack files"
2019-12-04 iannucci@chromium.org [bot_update] Also bootstrap in the case that there are 0 pack files

Created with:
  gclient setdep -r src/third_party/depot_tools@9212599f6aac

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/depot-tools-chromium-autoroll
Please CC agable@chromium.org on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

Bug: chromium:875523
Tbr: agable@chromium.org
Change-Id: I77c0d16e6ac98f793ba133a55e83ae3c067b18b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1952079Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#721822}

DEPS

@@ -891,7 +891,7 @@ deps = {
   },
 
   'src/third_party/depot_tools':
-    Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + 'a0b8c5dcf1890916119ed180ab936948ec62cba1',
+    Var('chromium_git') + '/chromium/tools/depot_tools.git' + '@' + '9212599f6aacbdbecd378814e63e236660ab42aa',
 
   'src/third_party/devtools-frontend/src':
     Var('chromium_git') + '/devtools/devtools-frontend' + '@' + Var('devtools_frontend_revision'),