Safe browsing v4 metadata fuzzer

The V4 metadata is just a repeated field of bytes->bytes. This is
unstructured data so we should probably fuzz it, even though it is
currently relatively simple. 

Note: I don't think the metadata parser currently depends on ICU, so
this fuzzer doesn't initialize it.

Bug: None
Change-Id: I26f791177dc0bf5b7a567a4f398b952188b06699
Reviewed-on: https://chromium-review.googlesource.com/727570
Commit-Queue: Charlie Harrison <[email protected]>
Reviewed-by: Varun Khaneja <[email protected]>
Cr-Commit-Position: refs/heads/master@{#510632}
3 files changed