Limit buffering in BufferingBytesConsumer

blink::BufferingBytesConsumer would continue buffering data until it ran out of memory and crashed. Make it buffer at most 55MB before applying backpressure instead.

Add web platform test for fetching a huge cacheable file to a stream and applying back-pressure.

BUG=40264318

Change-Id: I4fc43a0df6030ef404f06eabafac1bcb39b7e6b3 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5477147 Reviewed-by: Kouhei Ueno kouhei@chromium.org Commit-Queue: Adam Rice ricea@chromium.org Reviewed-by: Tsuyoshi Horo horo@chromium.org Cr-Commit-Position: refs/heads/main@{#1292266}