Remove deprecated StringBuffer.add, addAll and addCharCode.

utils/css/treebase.dart

Index: utils/css/treebase.dart
diff --git a/utils/css/treebase.dart b/utils/css/treebase.dart
index c5d517add1db9bae71607d3ee5bd1f31866fe2fa..7bdc3e6b3866a49ca4c146b3342bf16c83b4cef8 100644
--- a/utils/css/treebase.dart
+++ b/utils/css/treebase.dart
@@ -57,20 +57,20 @@ class TreeOutput {
 
   void write(String s) {
     for (int i=0; i < depth; i++) {
-      buf.add(' ');
+      buf.write(' ');
     }
-    buf.add(s);
+    buf.write(s);
   }
 
   void writeln(String s) {
     write(s);
-    buf.add('\n');
+    buf.write('\n');
   }
 
   void heading(String name, span) {
     write(name);
-    buf.add('  (${span.locationText})');
-    buf.add('\n');
+    buf.write('  (${span.locationText})');
+    buf.write('\n');
   }
 
   String toValue(value) {
@@ -95,14 +95,14 @@ class TreeOutput {
   void writeList(String label, List list) {
     write(label + ': ');
     if (list == null) {
-      buf.add('null');
-      buf.add('\n');
+      buf.write('null');
+      buf.write('\n');
     } else {
       for (var item in list) {
-        buf.add(item.toString());
-        buf.add(', ');
+        buf.write(item.toString());
+        buf.write(', ');
       }
-      buf.add('\n');
+      buf.write('\n');
     }
   }