Loads the Sass text for the given
url, or returns
this importer can't find the stylesheet it refers to.
url comes from a call to canonicalize for this importer.
When Sass encounters an
@import rule in a stylesheet, it first calls
canonicalize and load on the importer that first loaded that
stylesheet with the imported URL resolved relative to the stylesheet's
original URL. If either of those returns
null, it then calls
canonicalize and load on each importer in order with the URL as it
appears in the
If the importer finds a stylesheet at
url but it fails to load for some
reason, or if
url is uniquely associated with this importer but doesn't
refer to a real stylesheet, the importer may throw an exception that will
be wrapped by Sass. If the exception object has a
message property, it
will be used as the wrapped exception's message; otherwise, the exception
toString() will be used. This means it's safe for importers to
throw plain strings.
ImporterResult load(Uri url);