In rebaseline-cl, handle case when retry summary is not available.

third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot.py b/third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot.py
index 3417e269a2e4bfb24b01e3d7aff043e4a496c555..bc7b3b055b49f78347bf9f000c173c52e5e8e64a 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot.py
@@ -86,7 +86,8 @@ class BuildBot(object):
         both with and without ("ignored").
         """
         url_base = "%s/%s" % (self.builder_results_url_base(build.builder_name), build.build_number)
-        return self._fetch_file(url_base, 'retry_summary.json')
+        return NetworkTransaction(convert_404_to_None=True).run(
+            lambda: self._fetch_file(url_base, "retry_summary.json"))
 
     def accumulated_results_url_base(self, builder_name):
         return self.builder_results_url_base(builder_name) + "/results/layout-test-results"