Async Clipboard: Read/Write Blob->sequence<Blob>

- read(Blob) updated to read(sequence<Blob>).
- write() returns sequence<Blob> instead of Blob now.
- All available and valid types are returned in read() or allowed for write().
- Tests updated and added for these API changes.

Also:
- Updated header file function ordering.
- Duplicate MIME types not allowed on write (consistent w/existing clipboard).

Bug: 150835
Change-Id: I5b08e648a5313222552757dfa6fa0db6a7e46f68
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1471492
Commit-Queue: Darwin Huang <huangdarwin@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638905}
23 files changed