Allow 'noparent' in DEPS

In case of PartitionAlloc project in Chromium, there is a case that
it's useful to declare 'noparent' in the DEPS due to the situation
that a sub directory is exported to a standalone git project.

//base/allocator/partition_allocator/ (sub directory) is exported to
https://chromium.googlesource.com/chromium/src/base/allocator/partition_allocator.git

Change-Id: Ic51b6cd3928002962f25620b4d8797bed7802d1e
Bug: chromium:1151236
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3802719Reviewed-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Reviewed-by: Joanna Wang <jojwang@chromium.org>

gclient_eval.py

@@ -202,6 +202,14 @@ _GCLIENT_SCHEMA = schema.Schema(
         # Also see 'skip_child_includes' and 'specific_include_rules'.
         schema.Optional('include_rules'): [schema.Optional(basestring)],
 
+        # Optionally discards rules from parent directories, similar to
+        # "noparent" in OWNERS files. For example, if
+        # //base/allocator/partition_allocator has "noparent = True" then it
+        # will not inherit rules from //base/DEPS and //base/allocator/DEPS,
+        # forcing each //base/allocator/partition_allocator/{foo,bar,...} to
+        # declare all its dependencies.
+        schema.Optional('noparent'): bool,
+
         # Hooks executed before processing DEPS. See 'hooks' for more details.
         schema.Optional('pre_deps_hooks'): _GCLIENT_HOOKS_SCHEMA,