Add basic support for web fonts. Synchronous loading only
for now, and only deals with TTF format fonts.

For an example, try loading http://icons.marekventur.de
Fix missing license header in new file.
Address review comments.
Don't rely on font hint for format detection. Handle parsing comma
separated format hints. Fix oversight in mac code dealing with
creating web fonts from memory.
Update font face to new url parser.
Fix parsing invalid url, clean up font template matching.
Pass an argument to spawn_named_with_send_on_failure to support spawning native tasks.
Use spawn_named_with_send_on_failure for the RenderTask (fixes #2744).
Implement support for :disabled CSS selector
Implement support for :enabled CSS selector
Implement support for 'disabled' property in HTMLButtonElement
Implement support for 'disabled' property in HTMLFieldSetElement
Implement support for 'disabled' property in HTMLInputElement
Implement support for 'disabled' property in HTMLOptGroupElement
Implement support for 'disabled' property in HTMLOptionElement
Implement support for 'disabled' property in HTMLSelectElement
Implement support for 'disabled' property in HTMLTextAreaElement
Implement support for 'enabled' property in HTMLAnchorElement
Implement support for 'enabled' property in HTMLAreaElement
Implement support for 'enabled' property in HTMLLinkElement