GitLab

The are no unencodable characters in UTF-8, however previously callers
to blink::TextCoder::Encode had to pass a dummy UnencodableHandling
argument. Add a kNoUnencodables value to the UnencodableHandling which is
an explicit no-op. Also add DCHECKs that is is only used for UTF-8 or
UTF-16.

Convert callers to use kNoUnencodables where the encoding is statically
known to be UTF-8.

It's still valid to use other values for the UnencodableHandling
argument with UTF-8 or UTF-16; kNoUnencodables simply documents that it
makes no difference.

Change-Id: I5eebe4c76ae4006ee91f3884f94ec3b5e410685b
Reviewed-on: https://chromium-review.googlesource.com/1206055Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Joshua Bell <jsbell@chromium.org>
Commit-Queue: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589451}