Add charset declarations to non-ASCII tests
Add support for showing debug borders

This can help debug issues with the compositor and show when a page is
creating layers.
Merge pull request #2910 from kmcallister/charset

Add charset declarations to non-ASCII tests
Avoid an unnecessary clone of the base URL in parse_html().
Implement Window.screen.
Remove some unnecessary uses of the serialize module.
Merge pull request #2913 from Ms2ger/url-clone

Avoid an unnecessary clone of the base URL in parse_html(); r=jdm
Merge pull request #2914 from Ms2ger/screen

Implement Window.screen; r=jdm
Merge pull request #2912 from mrobinson/debug-borders

Add support for showing debug borders