Enable LibSass specs for @content args

[skip libsass]

spec/mixin/content/arguments/error/args_for_argless/error-libsass

@@ -0,0 +1,7 @@
+Error: wrong number of arguments (1 for 0) for `@content'
+        on line 2:3 of test.scss, in mixin `@content`
+        from line 2:3 of test.scss, in mixin `mixin`
+        from line 5:10 of test.scss
+>>   @content(value);
+
+   --^

spec/mixin/content/arguments/error/expected_args/error-libsass

@@ -0,0 +1,6 @@
+Error: Mixin @content is missing argument $arg1.
+        on line 2:3 of test.scss, in mixin `mixin`
+        from line 5:10 of test.scss
+>>   @content;
+
+   --^

spec/mixin/content/arguments/error/invalid_arglist/error-libsass

@@ -0,0 +1,5 @@
+Error: Invalid CSS after "...) using ($arg1:": expected expression (e.g. 1px, bold), was ") {}"
+        on line 5:32 of test.scss
+>> @include mixin() using ($arg1: ) {}
+
+   -------------------------------^

spec/mixin/content/arguments/error/invalid_named_arg/error-libsass

@@ -0,0 +1,7 @@
+Error: Mixin @content has no parameter named $invalid
+        on line 2:12 of test.scss, in mixin `@content`
+        from line 2:3 of test.scss, in mixin `mixin`
+        from line 5:10 of test.scss
+>>   @content($invalid: value);
+
+   -----------^

spec/mixin/content/arguments/error/missing_arglist/error-libsass

@@ -0,0 +1,5 @@
+Error: Invalid CSS after "...ude mixin using": expected "(", was "{}"
+        on line 5:16 of test.scss
+>> @include mixin using {}
+
+   ---------------^

spec/mixin/content/arguments/error/missing_parens/error-libsass

@@ -0,0 +1,5 @@
+Error: Invalid CSS after "...ude mixin using": expected "(", was "$arg1 {}"
+        on line 5:16 of test.scss
+>> @include mixin using $arg1 {}
+
+   ---------------^

spec/mixin/content/arguments/error/missing_using/error-libsass

@@ -0,0 +1,5 @@
+Error: Invalid CSS after "@include mixin()": expected ";", was "() {}"
+        on line 5:16 of test.scss
+>> @include mixin() () {}
+
+   ---------------^

spec/mixin/content/arguments/error/too_few_args/error-libsass

@@ -0,0 +1,6 @@
+Error: Mixin @content is missing argument $arg2.
+        on line 2:3 of test.scss, in mixin `mixin`
+        from line 5:10 of test.scss
+>>   @content(1);
+
+   --^

spec/mixin/content/arguments/error/too_many_args/error-libsass

@@ -0,0 +1,7 @@
+Error: wrong number of arguments (3 for 2) for `@content'
+        on line 2:3 of test.scss, in mixin `@content`
+        from line 2:3 of test.scss, in mixin `mixin`
+        from line 5:10 of test.scss
+>>   @content(1, 2, 3);
+
+   --^

spec/mixin/content/arguments/error/using_without_block/error-libsass

@@ -0,0 +1,5 @@
+Error: Invalid CSS after "... mixin using ()": expected "{", was ";"
+        on line 5:23 of test.scss
+>> @include mixin using ();
+
+   ----------------------^

spec/mixin/content/arguments/options.yml

@@ -1,5 +1,3 @@
 ---
 :ignore_for:
 - ruby-sass
-:todo:
-- libsass # sass/libsass#2723