Use the current parser location for CSS error

… rather than the start location of the current construct.
This likely places the error just *after* of the unexpected token
whereas before would be best, but that’s likely a much bigger change.

See https://bugzilla.mozilla.org/show_bug.cgi?id=1378861

components/style/stylesheets/viewport_rule.rs

@@ -370,7 +370,7 @@ impl ViewportRule {
                 }
                 Err(err) => {
                     let error = ContextualParseError::UnsupportedViewportDescriptorDeclaration(err.slice, err.error);
-                    context.log_css_error(error_context, err.location, error);
+                    context.log_css_error(error_context, parser.input.current_source_location(), error);
                 }
             }
         }