Remove deprecated StringBuffer.add, addAll and addCharCode.

sdk/lib/core/expect.dart

Index: sdk/lib/core/expect.dart
diff --git a/sdk/lib/core/expect.dart b/sdk/lib/core/expect.dart
index bf9053a0a504c9b1f4aa4825bda5a2500ef98a48..0302d3deef99c3d3309afb89374e0e9afc01ef27 100644
--- a/sdk/lib/core/expect.dart
+++ b/sdk/lib/core/expect.dart
@@ -252,20 +252,20 @@ class Expect {
     StringBuffer sb = new StringBuffer("Expect.setEquals($msg) fails");
     // Report any missing items.
     if (!missingSet.isEmpty) {
-      sb.add('\nExpected collection does not contain: ');
+      sb.write('\nExpected collection does not contain: ');
     }
 
     for (final val in missingSet) {
-      sb.add('$val ');
+      sb.write('$val ');
     }
 
     // Report any extra items.
     if (!extraSet.isEmpty) {
-      sb.add('\nExpected collection should not contain: ');
+      sb.write('\nExpected collection should not contain: ');
     }
 
     for (final val in extraSet) {
-      sb.add('$val ');
+      sb.write('$val ');
     }
     _fail(sb.toString());
   }