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

tools/android/loading/sandwich_swr.py

Index: tools/android/loading/sandwich_swr.py
diff --git a/tools/android/loading/sandwich_swr.py b/tools/android/loading/sandwich_swr.py
index 46910c4078cd3f09bc8b361f35ad6a72ceaf87b7..96730ba5b46507e642f1ffb2c6f0b126f7bbab36 100644
--- a/tools/android/loading/sandwich_swr.py
+++ b/tools/android/loading/sandwich_swr.py
@@ -26,7 +26,8 @@ def _BuildPatchedCache(original_cache_run_path, original_cache_archive_path,
   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.BatchCacheBackend(
+        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:
@@ -40,6 +41,7 @@ def _BuildPatchedCache(original_cache_run_path, original_cache_archive_path,
       raw_headers = request.GetRawResponseHeaders()
       cache_backend.UpdateRawResponseHeaders(request.url, raw_headers)
       patch_count += 1
+    cache_backend.ProcessBatch()
     chrome_cache.ZipDirectoryContent(cache_path, cache_archive_dest_path)
   logging.info('Patched %d cached resources out of %d' % (
       patch_count, len(cache_keys)))