Update buildbots to parse new telemetry JSON format.

scripts/slave/performance_log_processor.py

Index: scripts/slave/performance_log_processor.py
diff --git a/scripts/slave/performance_log_processor.py b/scripts/slave/performance_log_processor.py
index 5be386aded4d1fcd9e538c401f8c414145e874f9..29682f508ecdbcacdf9b6fb5f7f8846ae3cb41af 100644
--- a/scripts/slave/performance_log_processor.py
+++ b/scripts/slave/performance_log_processor.py
@@ -112,6 +112,10 @@ class PerformanceLogProcessor(object):
 
     self._percentiles = [.1, .25, .5, .75, .90, .95, .99]
 
+  def IsChartJson(self):  # pylint: disable=R0201
+    """This is not the new telemetry --chartjson output format."""
+    return False
+
   def PerformanceLogs(self):
     if not self._finalized:
       self._FinalizeProcessing()