Add support for small-caps font-variant.

Ref: 2554.
Disable non_snake_case warnings in devtools
Fix other warnings in devtools
Avoid an unnecessary string allocation in allow_cross_origin_request.
Add fixme comment for future work, make scale factor a constant.
Merge pull request #3461 from mbrubeck/warnings

Fix misc warnings in devtools crates. r=jdm
Handle null strings in Namespace::new.

This also avoids a string copy in the rare case of an unrecognized namespace.
Merge pull request #3462 from Ms2ger/as-slice

Avoid an unnecessary string allocation in allow_cross_origin_request; r=jdm
Remove redundant into_string() calls.
layout: Implement `white-space: nowrap`.

Improves the Reddit header.
Merge pull request #3459 from glennw/small-caps

Add support for small-caps font-variant.
Merge pull request #3466 from Ms2ger/into_string

Remove redundant into_string() calls.; r=jdm
Merge pull request #3458 from pcwalton/whitespace-nowrap

layout: Implement `white-space: nowrap`.
Merge pull request #3465 from Ms2ger/ns

Handle null strings in Namespace::new.