Add git_dependencies flag to DEPS

This change adds `git_dependencies` flag to the DEPS. This will be used to track the submodule migration state.

Design Doc: go/depot-tools-on-submodules
Change-Id: I547ad8ebbce2535960d4b6e00c0b14c00118f544
Bug: 1429149
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/4591777
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>
diff --git a/gclient_eval.py b/gclient_eval.py
index 5571946..ac4f49b 100644
--- a/gclient_eval.py
+++ b/gclient_eval.py
@@ -24,6 +24,13 @@
   basestring = str
 
 
+# git_dependencies migration states. Used within the DEPS file to indicate
+# the current migration state.
+DEPS = 'DEPS'
+SYNC = 'SYNC'
+SUBMODULES = 'SUBMODULES'
+
+
 class ConstantString(object):
   def __init__(self, value):
     self.value = value
@@ -156,6 +163,11 @@
 
 _GCLIENT_SCHEMA = schema.Schema(
     _NodeDictSchema({
+        # Current state of the git submodule migration.
+        # git_dependencies = [DEPS (default) | SUBMODULES | SYNC]
+        schema.Optional('git_dependencies'):
+        schema.Or(DEPS, SYNC, SUBMODULES),
+
         # List of host names from which dependencies are allowed (allowlist).
         # NOTE: when not present, all hosts are allowed.
         # NOTE: scoped to current DEPS file, not recursive.
@@ -169,21 +181,25 @@
         #
         #   Var(): allows variable substitution (either from 'vars' dict below,
         #          or command-line override)
-        schema.Optional('deps'): _GCLIENT_DEPS_SCHEMA,
+        schema.Optional('deps'):
+        _GCLIENT_DEPS_SCHEMA,
 
         # Similar to 'deps' (see above) - also keyed by OS (e.g. 'linux').
         # Also see 'target_os'.
-        schema.Optional('deps_os'): _NodeDictSchema({
+        schema.Optional('deps_os'):
+        _NodeDictSchema({
             schema.Optional(basestring): _GCLIENT_DEPS_SCHEMA,
         }),
 
         # Dependency to get gclient_gn_args* settings from. This allows these
         # values to be set in a recursedeps file, rather than requiring that
         # they exist in the top-level solution.
-        schema.Optional('gclient_gn_args_from'): basestring,
+        schema.Optional('gclient_gn_args_from'):
+        basestring,
 
         # Path to GN args file to write selected variables.
-        schema.Optional('gclient_gn_args_file'): basestring,
+        schema.Optional('gclient_gn_args_file'):
+        basestring,
 
         # Subset of variables to write to the GN args file (see above).
         schema.Optional('gclient_gn_args'): [schema.Optional(basestring)],
@@ -191,12 +207,12 @@
         # Hooks executed after gclient sync (unless suppressed), or explicitly
         # on gclient hooks. See _GCLIENT_HOOKS_SCHEMA for details.
         # Also see 'pre_deps_hooks'.
-        schema.Optional('hooks'): _GCLIENT_HOOKS_SCHEMA,
+        schema.Optional('hooks'):
+        _GCLIENT_HOOKS_SCHEMA,
 
         # Similar to 'hooks', also keyed by OS.
-        schema.Optional('hooks_os'): _NodeDictSchema({
-            schema.Optional(basestring): _GCLIENT_HOOKS_SCHEMA
-        }),
+        schema.Optional('hooks_os'):
+        _NodeDictSchema({schema.Optional(basestring): _GCLIENT_HOOKS_SCHEMA}),
 
         # Rules which #includes are allowed in the directory.
         # Also see 'skip_child_includes' and 'specific_include_rules'.
@@ -208,21 +224,22 @@
         # 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,
+        schema.Optional('noparent'):
+        bool,
 
         # Hooks executed before processing DEPS. See 'hooks' for more details.
-        schema.Optional('pre_deps_hooks'): _GCLIENT_HOOKS_SCHEMA,
+        schema.Optional('pre_deps_hooks'):
+        _GCLIENT_HOOKS_SCHEMA,
 
         # Recursion limit for nested DEPS.
-        schema.Optional('recursion'): int,
+        schema.Optional('recursion'):
+        int,
 
         # Allowlists deps for which recursion should be enabled.
         schema.Optional('recursedeps'): [
-            schema.Optional(schema.Or(
-                basestring,
-                (basestring, basestring),
-                [basestring, basestring]
-            )),
+            schema.Optional(
+                schema.Or(basestring, (basestring, basestring),
+                          [basestring, basestring])),
         ],
 
         # Blocklists directories for checking 'include_rules'.
@@ -230,9 +247,8 @@
 
         # Mapping from paths to include rules specific for that path.
         # See 'include_rules' for more details.
-        schema.Optional('specific_include_rules'): _NodeDictSchema({
-            schema.Optional(basestring): [basestring]
-        }),
+        schema.Optional('specific_include_rules'):
+        _NodeDictSchema({schema.Optional(basestring): [basestring]}),
 
         # List of additional OS names to consider when selecting dependencies
         # from deps_os.
@@ -241,17 +257,19 @@
         # For recursed-upon sub-dependencies, check out their own dependencies
         # relative to the parent's path, rather than relative to the .gclient
         # file.
-        schema.Optional('use_relative_paths'): bool,
+        schema.Optional('use_relative_paths'):
+        bool,
 
         # For recursed-upon sub-dependencies, run their hooks relative to the
         # parent's path instead of relative to the .gclient file.
-        schema.Optional('use_relative_hooks'): bool,
+        schema.Optional('use_relative_hooks'):
+        bool,
 
         # Variables that can be referenced using Var() - see 'deps'.
-        schema.Optional('vars'): _NodeDictSchema({
-            schema.Optional(basestring): schema.Or(ConstantString,
-                                                   basestring,
-                                                   bool),
+        schema.Optional('vars'):
+        _NodeDictSchema({
+            schema.Optional(basestring):
+            schema.Or(ConstantString, basestring, bool),
         }),
     }))