Bump up chunk size from 4 to 64 MB to speed up CIPD verifyUploadTask.
Bump up chunk size from 4 to 64 MB to speed up CIPD verifyUploadTask.

The small chunk size originates from limitations to URLFetch in GAE Standard, which no longer apply to modern runtimes.

BUG=1261988
Change-Id: If585c7ef253d0adf1cc3b06a82af418e9c643eb3
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3863058
Commit-Queue: Jani Patokallio <646c3fad45809c2a958cce7b5df636ef8de93e7d@google.com>
Reviewed-by: Michal Kiedys <472a1e6216c9a44ed7bded64510d0626a6b6ca20@google.com>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go