gpu: Prune old TransferCache entries

Business logic changes:
* Transfer cache will post hard-coded 30s delayed task to clear
  entries that are older than 30s
* Transfer cache will only have one pending task, but keeps track
  of requests to post more tasks while one is pending and post again
  when the current pending task runs. This means old entry can live
  close to 60s at the longest end.
* Pruning entries is similar to enforcing memory limits.
* "Flush" after pruning at the end, which is implemented by scheduling
  GrCacheController to run (with up to 1s delay)
* Change GrCacheController to flush for vulkan as well by flush
  (with a callback) and submit.

Changes for experimentation:
* Client side purge kPurgeOldCacheEntriesOnTimer moved to //gpu
* Add new feature kPruneOldTransferCacheEntries
* * If kPurgeOldCacheEntriesOnTimer is disabled, both client and
    service side logic are disabled
* * Otherwise, kPruneOldTransferCacheEntries controls whether to use
    service- or client-side pruning
* * This is to support hold back experiment for client side purge
* Add kPruneOldTransferCacheEntries to webview flags
* Enable kPruneOldTransferCacheEntries in fieldtrial_testing_config.json

Bug: 1442988
Change-Id: Iea38803b57cb4089f7bdf3f4b00526019c757fcc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5074796
Commit-Queue: Bo Liu <boliu@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Reviewed-by: Benoit Lize <lizeb@chromium.org>
Reviewed-by: Thiabaud Engelbrecht <thiabaud@google.com>
Cr-Commit-Position: refs/heads/main@{#1233700}

• android_webview/java/src/org/chromium/android_webview/common/ProductionSupportedFlagList.java[diff]
• cc/tiles/gpu_image_decode_cache.cc[diff]
• cc/tiles/gpu_image_decode_cache.h[diff]
• cc/tiles/gpu_image_decode_cache_unittest.cc[diff]
• gpu/command_buffer/service/gr_cache_controller.cc[diff]
• gpu/command_buffer/service/service_transfer_cache.cc[diff]
• gpu/command_buffer/service/service_transfer_cache.h[diff]
• gpu/command_buffer/service/service_transfer_cache_unittest.cc[diff]
• gpu/command_buffer/service/shared_context_state.cc[diff]
• gpu/config/gpu_finch_features.cc[diff]
• gpu/config/gpu_finch_features.h[diff]
• testing/variations/fieldtrial_testing_config.json[diff]