/deep/, >>>, ::shadow are unsupported

[har79]

These selectors are deprecated: https://code.google.com/p/chromium/issues/detail?id=489954
however there isn't a replacement yet and there are still discussions what form that will take so they'll likely be around for quite a while.

csslib's parsing fails when it comes across one of these, with a message of the form
"error on line 33, column 17 of foo.css: expected {, but found /
foo /deep/ #bar {"
from https://github.com/dart-lang/csslib/blob/master/lib/parser.dart#L307

I'll try and come up with a patch, although it'll probably not be in the next couple of weeks.

For future reference, I've traced where I believe the error is coming from:
_errorExpected('{'), l299
_eat(TokenKind.LBRACE), l1042
_processDeclarations(), l985

_processDeclarations() tries to handle "/deep/", because it's not consumed by:
processSelectorGroup(), l981
processSelector(), /1186
simpleSelectorSequence(simpleSequences.length == 0), l1206
simpleSelector(), l1254

[ochafik]

Any update on this? There seems to be still lots of /deep/ selectors in the wild, as Angular2's static CSS transforms support it.

[MonamAgarwal]

Any update on this? This seems to be causing problem with css-mirroring transformer in scissors also.