pkg/csslib: types, fixes, cleanup

pkg/csslib/lib/src/tree_base.dart

Index: pkg/csslib/lib/src/tree_base.dart
diff --git a/pkg/csslib/lib/src/tree_base.dart b/pkg/csslib/lib/src/tree_base.dart
index 29b955dcd229f672c61c7ab5182600df3a20e686..e61a06c90ad8c39e433dbcb5667bfe40f34a5e12 100644
--- a/pkg/csslib/lib/src/tree_base.dart
+++ b/pkg/csslib/lib/src/tree_base.dart
@@ -9,14 +9,14 @@ part of csslib.visitor;
  */
 abstract class TreeNode {
   /** The source code this [TreeNode] represents. */
-  Span span;
+  final Span span;
 
-  TreeNode(this.span) {}
+  TreeNode(this.span);
 
   TreeNode clone();
 
   /** Classic double-dispatch visitor for implementing passes. */
-  visit(VisitorBase visitor);
+  void visit(VisitorBase visitor);
 
   /** A multiline string showing the node and its children. */
   String toDebugString() {
@@ -36,7 +36,7 @@ abstract class Expression extends TreeNode {
 class TreeOutput {
   int depth = 0;
   final StringBuffer buf = new StringBuffer();
-  var printer;
+  VisitorBase printer;
 
   void write(String s) {
     for (int i=0; i < depth; i++) {
@@ -77,7 +77,7 @@ class TreeOutput {
     writeln('${label}: ${v}');
   }
 
-  void writeList(String label, List list) {
+  void writeList(String label, List<TreeNode> list) {
     write('${label}: ');
     if (list == null) {
       buf.write('null');
@@ -91,7 +91,7 @@ class TreeOutput {
     }
   }
 
-  void writeNodeList(String label, List list) {
+  void writeNodeList(String label, List<TreeNode> list) {
     writeln('${label} [');
     if (list != null) {
       depth += 1;