Regenerate MANIFEST.json when WPT tests are run

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
index b739d1dc809046dc84a7a795d540023b9e047d67..2fdf11717b1a1bb7a1a99f0dc501d1dd6928997d 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
@@ -36,6 +36,7 @@ import difflib
 import errno
 import functools
 import json
+import hashlib
 import logging
 import optparse
 import re
@@ -739,8 +740,32 @@ class Port(object):
 
     @memoized
     def _wpt_manifest(self):
-        path = self._filesystem.join(self.layout_tests_dir(), 'external', 'wpt', 'MANIFEST.json')
-        return json.loads(self._filesystem.read_text_file(path))
+        manifest_path = self._filesystem.join(self.layout_tests_dir(), 'external', 'wpt', 'MANIFEST.json')
+
+        original_hash = self._get_manifest_hash(manifest_path)
+        self._generate_manifest()
+        updated_hash = self._get_manifest_hash(manifest_path)
+
+        if original_hash != updated_hash:
+            _log.warning('MANIFEST.json has been updated to reflect changes in external/wpt!')
+
+        return json.loads(self._filesystem.read_text_file(manifest_path))
+
+    def _get_manifest_hash(self, manifest_path):
+        hash_context = hashlib.md5()
+
+        manifest_buffer = self._filesystem.read_binary_file(manifest_path)
+        assert manifest_buffer
+
+        hash_context.update(manifest_buffer)
+        return hash_context.hexdigest()
+
+    def _generate_manifest(self):
+        wpt_path = self._webkit_finder.path_from_webkit_base('LayoutTests', 'external', 'wpt')
+        manifest_path = self._webkit_finder.path_from_webkit_base(
+            'Tools', 'Scripts', 'webkitpy', 'thirdparty', 'wpt', 'wpt', 'manifest')
+        _log.info('Generating MANIFEST.json')
+        self._executive.run_command([manifest_path, '--work', '--tests-root', wpt_path])
 
     def _manifest_items_for_path(self, path_in_wpt):
         """Returns a manifest item for the given WPT path, or None if not found.