Bug 1476053 - Handle invalid json in metadata updates, r=ato

Sometimes we get errors that result in invalid json in the logs.
There's nothing reasonable to do about this during metadata updates
so just skip it

MozReview-Commit-ID: 4QuM7M3lXGv

--HG--
extra : rebase_source : 7e828a32c0a05338ff050f16ab6a91761e58d9b0

testing/web-platform/tests/tools/wptrunner/wptrunner/metadata.py

@@ -250,7 +250,11 @@ class ExpectedUpdater(object):
     def update_from_raw_log(self, log_file):
         action_map = self.action_map
         for line in log_file:
-            data = json.loads(line)
+            try:
+                data = json.loads(line)
+            except ValueError:
+                # Just skip lines that aren't json
+                continue
             action = data["action"]
             if action in action_map:
                 action_map[action](data)