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..7f41bedf18ef41105bc988ba8fdefb8d90885db1 100644
--- a/tools/android/loading/sandwich_swr.py
+++ b/tools/android/loading/sandwich_swr.py
@@ -26,20 +26,21 @@ 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_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)
-      raw_headers = request.GetRawResponseHeaders()
-      cache_backend.UpdateRawResponseHeaders(request.url, raw_headers)
-      patch_count += 1
+    with chrome_cache.OnlineCacheBackend(
+        cache_path, chrome_cache.CacheBackendType.SIMPLE) as cache_backend:
+      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)
+        raw_headers = request.GetRawResponseHeaders()
+        cache_backend.UpdateRawResponseHeaders(request.url, raw_headers)
+        patch_count += 1
     chrome_cache.ZipDirectoryContent(cache_path, cache_archive_dest_path)
   logging.info('Patched %d cached resources out of %d' % (
       patch_count, len(cache_keys)))