Gss converter fails to convert some conditionals.

The converter converts conditionals with negation improperly.
The following conditional:
@if !property foo bar {}
was converted to
@if (!is("property", "foo") || !is("property", "bar")) {}
instead of
@if (!is("property", "foo") && !is("property", "bar")) {}

Bug: issue 9020
Change-Id: I80cdcf781d224142c3ad981ecde3133ff4ac86ed
Css to GSS converter failed to recognize variables in font rules.

Bug: issue 9014
Change-Id: I092c3f87c077d8e0d9d78e725af9008f1a741613