Bug 1405413 - Pre: Allow toolchain tasks to (un)set sparse-profile. r=glandium

Specifying anything but "toolchain-build" appears to have cache
errors, which I cannot understand.  These cache errors can be
addressed in follow-up, if and when toolchain tasks require new sparse
profiles.  But specifying `null` avoids the sparse profile details
entirely, which works nicely for `android-gradle-dependencies`, which
is build-like and requires a fairly complete checkout.

MozReview-Commit-ID: L3R8UIDjgqW

--HG--
extra : rebase_source : 096a180238d1b5eeffbb0e2d9d538def162e877f

taskcluster/taskgraph/transforms/job/toolchain.py

@@ -50,6 +50,13 @@ toolchain_run_schema = Schema({
     # If true, tc-vcs will be enabled.  Not supported on Windows.
     Required('tc-vcs', default=True): bool,
 
+    # Sparse profile to give to checkout using `run-task`.  If given,
+    # a filename in `build/sparse-profiles`.  Defaults to
+    # "toolchain-build", i.e., to
+    # `build/sparse-profiles/toolchain-build`.  If `None`, instructs
+    # `run-task` to not use a sparse profile at all.
+    Required('sparse-profile', default='toolchain-build'): Any(basestring, None),
+
     # Paths/patterns pointing to files that influence the outcome of a
     # toolchain build.
     Optional('resources'): [basestring],
@@ -150,10 +157,15 @@ def docker_worker_toolchain(config, job, taskdesc):
     if args:
         args = ' ' + shell_quote(*args)
 
+    sparse_profile = []
+    if run.get('sparse-profile'):
+        sparse_profile = ['--sparse-profile',
+                          'build/sparse-profiles/{}'.format(run['sparse-profile'])]
+
     worker['command'] = [
         '/builds/worker/bin/run-task',
         '--vcs-checkout=/builds/worker/workspace/build/src',
-        '--sparse-profile', 'build/sparse-profiles/toolchain-build',
+    ] + sparse_profile + [
         '--',
         'bash',
         '-c',