FileAPI: Add more WPT for Blob read methods.

This change adds 3 new tests:
1. Make sure that garbage collection of the Blob will not break
consumption of it's readable stream.
2. Make sure that concurrent reads via the text() method work.
3. Make sure that concurrent reads via the arrayBuffer() method work.

Bug: 945893
Change-Id: Ie1fb2095ba921d0b8638fc6c53264938bc9e871c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1584703
Commit-Queue: Jarryd Goodman <jarrydg@chromium.org>
Auto-Submit: Jarryd Goodman <jarrydg@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654330}
3 files changed