pre-upload: split json check into a hook

BUG=chromium:466264
TEST=`./pre-upload_unittest.py` passes

Change-Id: I022809a1db3c4d48a8b3138a9453c39770303f0e
Reviewed-on: https://chromium-review.googlesource.com/262013
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Trybot-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Steve Fung <stevefung@chromium.org>
diff --git a/pre-upload.py b/pre-upload.py
index 7178a05..65c6afa 100755
--- a/pre-upload.py
+++ b/pre-upload.py
@@ -1124,7 +1124,6 @@
 # A dictionary of project-specific hooks(callbacks), indexed by project name.
 # dict[project] = [callback1, callback2]
 _PROJECT_SPECIFIC_HOOKS = {
-    "chromeos/autotest-tools": [_run_json_check],
     "chromeos/platform/ec-private": [_run_checkpatch_ec,
                                      _check_change_has_branch_field],
     "chromeos/third_party/intel-framework": [_check_change_has_branch_field],
@@ -1153,6 +1152,7 @@
 # that the flag controls (value).
 _HOOK_FLAGS = {
     'stray_whitespace_check': _check_no_stray_whitespace,
+    'json_check': _run_json_check,
     'long_line_check': _check_no_long_lines,
     'cros_license_check': _check_license,
     'tab_check': _check_no_tabs,