[BlobURL] Re-enable new blob URL architecture by default

This was enabled and then disabled due to an increase in
renderer hangs, but after investigating further it seems
plausible that this higher (but stable) number of
renderer hangs is inherent in using a synchronous Mojo
interface method of a navigation-associated interface
between the renderer and the browser process UI thread
(or at least is a side effect of some unknown issue that
causes the browser process to not respond to the messages
in a timely manner).

This requires temporarily disabling
kRestrictCanAccessDataForOriginToUIThread due to issues
that arise when both flags are enabled. For more info,
see:
 - https://chromium-review.googlesource.com/c/chromium/src/+/4764617/comments/850fbb6b_b25fed3c
 - https://bugs.chromium.org/p/chromium/issues/detail?id=764958#c54

Bug: 764958, 1407944
Change-Id: If287568c4beb9ee8faabd4ac166ebe4594095734
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4762807
Reviewed-by: Adam Langley <agl@chromium.org>
Commit-Queue: Andrew Williams <awillia@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1184679}

• content/common/features.cc[diff]
• net/base/features.cc[diff]