Hoist ParseErrorReporter into style and remove the dependency on msg.

The pipeline id stuff is currently unused. If someone needs it, they can add
an additional trait bound on their css error reporter to get the pipeline id.

components/style/error_reporting.rs

@@ -0,0 +1,25 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use cssparser::{Parser, SourcePosition};
+use log;
+
+pub trait ParseErrorReporter {
+    fn report_error(&self, input: &mut Parser, position: SourcePosition, message: &str);
+    fn clone(&self) -> Box<ParseErrorReporter + Send + Sync>;
+}
+
+pub struct StdoutErrorReporter;
+impl ParseErrorReporter for StdoutErrorReporter {
+    fn report_error(&self, input: &mut Parser, position: SourcePosition, message: &str) {
+         if log_enabled!(log::LogLevel::Info) {
+             let location = input.source_location(position);
+             info!("{}:{} {}", location.line, location.column, message)
+         }
+    }
+
+    fn clone(&self) -> Box<ParseErrorReporter + Send + Sync> {
+        box StdoutErrorReporter
+    }
+}