Bug 1390700 - Sparse checkout profiles for mach and taskgraph; r=dustin

Mercurial's sparse checkout support allows "profile" files defining
what's in sparse checkouts to be defined in-tree. This convenient
feature means you simply need to point a client at a path inside the
repository and it dynamically resolves what files to include in the
checkout. As you update revisions, the "profile" pulls in updates
to the underlying file.

We introduce 2 sparse profiles: 1 for mach and another for taskgraph.

The goal of the "mach" profile is to provide enough files to run
`mach`. If you activate this profile and run `mach`, it runs without
error. But there are practically no commands available. So it isn't
terribly useful.

The "taskgraph" profile allows us to run `mach taskgraph`. This
profile demonstrates a sparse profile feature: including other
profiles. The "taskgraph" profile is thus a union of "mach" and
its own entries.

There is definitely some fat in these profiles. I didn't feel like
chasing the long tail and getting overly granular with the profiles.
If we want to optimize later, we can do that.

For reference:

Full checkout: ~234,000 files
mach:            ~2,000 files
taskgraph:       ~3,600 files

MozReview-Commit-ID: 7pALt0MwHfE

--HG--
extra : rebase_source : 1a4ba4b8a63c522dab2841e2c0019501476da2fe

build/sparse-profiles/mach

@@ -0,0 +1,12 @@
+[include]
+# Various mach commands call config.guess to resolve the default objdir name.
+path:build/autoconf/config.guess
+# Used for bootstrapping the mach driver.
+path:build/mach_bootstrap.py
+path:build/virtualenv_packages.txt
+path:mach
+# Various dependencies. There is room to trim fat, especially in
+# third_party/python.
+path:python/
+path:testing/mozbase/
+path:third_party/python/

build/sparse-profiles/taskgraph

@@ -0,0 +1,24 @@
+%include build/sparse-profiles/mach
+
+[include]
+# This file is read as part of validating the taskgraph.
+path:browser/locales/all-locales
+
+# Lots of random files in here are read. Just pull in the whole thing.
+path:build/
+
+# This file is read as part of validating the taskgraph.
+path:mobile/locales/l10n-changesets.json
+
+# The main meat of this profile.
+path:taskcluster/
+
+# Various files in these directories are read by taskgraph. Just pull
+# them all in.
+path:testing/config/tooltool-manifests/
+path:testing/mozharness/
+path:tools/lint/
+
+# Tooltool manifests also need to be opened. Assume they
+# are all somewhere in "tooltool-manifests" directories.
+glob:**/tooltool-manifests/**