Add a 4k 60 fps vp9 smpte bars video to telemetry tests.

tools/perf/metrics/system_memory.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from telemetry.value import scalar
 
 from metrics import memory
 from metrics import Metric
 
 
@@ skipping 99 matching lines @@
         not start_memory_stats[process_type]):
       memory_stats[process_type] = end_process_memory
       continue
 
     if not isinstance(end_process_memory, dict):
       start_value = start_memory_stats[process_type] or 0
       memory_stats[process_type] = end_process_memory - start_value
     else:
       for metric in end_process_memory:
         end_value = end_process_memory[metric]
-        start_value = start_memory_stats[process_type][metric] or 0
+        start_value = start_memory_stats[process_type].get(metric, 0)
         if 'Peak' in metric:
           memory_stats[process_type][metric] = end_value
         else:
           memory_stats[process_type][metric] = end_value - start_value
   return memory_stats