git-sync-deps handles recursive DEPS

NOTRY=true
R=mtklein@google.com, borenet@google.com

Author: halcanary@google.com

Review URL: https://codereview.chromium.org/468113003
diff --git a/tools/git-sync-deps b/tools/git-sync-deps
index 22309bd..717ab38 100755
--- a/tools/git-sync-deps
+++ b/tools/git-sync-deps
@@ -194,6 +194,10 @@
 
   multithread(git_checkout_to_directory, list_of_arg_lists)
 
+  for directory in deps.get('recursedeps', []):
+    recursive_path = os.path.join(deps_file_directory, directory, 'DEPS')
+    git_sync_deps(recursive_path, deps_os_list, verbose)
+
 
 def multithread(function, list_of_arg_lists):
   # for args in list_of_arg_lists: