Increase benchmark I/O timeout to 20 minutes

This is a bandaid fix to address the problem that some story whose trace processing
takes more than 10 minutes to process.

crbug.com/810060 is opened for tracking reducing the time of trace processing.

Bug:805922
Change-Id: Id7b8a860f26460d49901ef4ebe0fee536b0029fd

NOTRY=true  # All testings are covered by PRESUBMIT

Change-Id: Id7b8a860f26460d49901ef4ebe0fee536b0029fd
Reviewed-on: https://chromium-review.googlesource.com/907313
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Reviewed-by: Emily Hanley <eyaich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535109}