Add BuildBotClient to abstract http/logdog access

tools/gardening/lib/src/buildbot_loading.dart

Index: tools/gardening/lib/src/buildbot_loading.dart
diff --git a/tools/gardening/lib/src/buildbot_loading.dart b/tools/gardening/lib/src/buildbot_loading.dart
index 35cf6d7c09ff799470ad077bc86ea2358469b355..9a2d53ae7751e740fa65e6ae4c81eeeaaf69fd21 100644
--- a/tools/gardening/lib/src/buildbot_loading.dart
+++ b/tools/gardening/lib/src/buildbot_loading.dart
@@ -113,7 +113,8 @@ BuildResult parseTestStepResult(BuildUri buildUri, String text) {
       }
     }
   }
-  return new BuildResult(buildUri, buildNumber, results, failures, timings);
+  return new BuildResult(buildUri, buildNumber ?? buildUri.absoluteBuildNumber,
+      results, failures, timings);
 }
 
 /// Create the [Timing]s for the [line] as found in the top-20 timings of a