sandwich: Use cachetool's batch mode to speed-up cache processing.

tools/android/loading/sandwich_swr.py

 # Copyright 2016 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.
 
 import csv
 import logging
 import os
 import shutil
 
 import chrome_cache
 import common_util
 import loading_trace
 import request_track
 import sandwich_metrics
 import sandwich_runner
 import task_manager
 
 
 def _BuildPatchedCache(original_cache_run_path, original_cache_archive_path,
       cache_archive_dest_path):
   CACHE_CONTROL_VALUE = 'max-age=0,stale-while-revalidate=315360000'
   trace_path = os.path.join(
       original_cache_run_path, '0', sandwich_runner.TRACE_FILENAME)
   trace = loading_trace.LoadingTrace.FromJsonFile(trace_path)
   patch_count = 0
   with common_util.TemporaryDirectory(prefix='sandwich_tmp') as tmp_path:
     cache_path = os.path.join(tmp_path, 'cache')
     chrome_cache.UnzipDirectoryContent(original_cache_archive_path, cache_path)
-    cache_backend = chrome_cache.CacheBackend(cache_path, 'simple')
+    cache_backend = chrome_cache.CacheBackend(
+        cache_path, chrome_cache.CacheBackendType.Simple)
     cache_keys = set(cache_backend.ListKeys())
     for request in trace.request_track.GetEvents():
       if request.url not in cache_keys:
         continue
       caching_policy = request_track.CachingPolicy(request)
       assert caching_policy.IsCacheable()
       freshness = caching_policy.GetFreshnessLifetimes()
       if freshness[0] == 0:
         continue
       request.SetHTTPResponseHeader('cache-control', CACHE_CONTROL_VALUE)
@@ skipping 103 matching lines @@
 
       run_metrics_list.sort(key=lambda e: e['repeat_id'])
       with open(ExtractMetrics.path, 'w') as csv_file:
         writer = csv.DictWriter(csv_file, fieldnames=(additional_column_names +
                                     sandwich_metrics.COMMON_CSV_COLUMN_NAMES))
         writer.writeheader()
         for trace_metrics in run_metrics_list:
           writer.writerow(trace_metrics)
 
     self._common_builder.default_final_tasks.append(ExtractMetrics)