[tools/perf] Trim down story name that has more than 180 charaters

tools/perf/page_sets/profile_safe_urls.py

Index: tools/perf/page_sets/profile_safe_urls.py
diff --git a/tools/perf/page_sets/profile_safe_urls.py b/tools/perf/page_sets/profile_safe_urls.py
index d64fa207d3f39d51666262ca433b1a5d2efe33bc..0e72cd3a601585092ec26ed1ee5d8a6a9a7d1584 100644
--- a/tools/perf/page_sets/profile_safe_urls.py
+++ b/tools/perf/page_sets/profile_safe_urls.py
@@ -11,6 +11,9 @@ class ProfileSafeUrlPage(page_module.Page):
   def __init__(self, url, page_set):
     super(ProfileSafeUrlPage, self).__init__(
         url=url,
+        # Make sure story name is not too long and has type 'str' instead of
+        # 'unicode'.
+        name=str(url[:140]),
         page_set = page_set,
         shared_page_state_class=shared_page_state.SharedDesktopPageState,
         credentials_path = 'data/credentials.json')