Remove deprecated StringBuffer.add, addAll and addCharCode.

sdk/lib/_internal/compiler/implementation/constants.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js;
 
 abstract class ConstantVisitor<R> {
   R visitSentinel(SentinelConstant constant);
   R visitFunction(FunctionConstant constant);
   R visitNull(NullConstant constant);
@@ skipping 110 matching lines @@
   factory NullConstant() => const NullConstant._internal();
   const NullConstant._internal();
   bool isNull() => true;
   get value => null;
 
   DartType computeType(Compiler compiler) {
     return compiler.nullClass.computeType(compiler);
   }
 
   void _writeJsCode(CodeBuffer buffer, ConstantHandler handler) {
-    buffer.add(JsNull);
+    buffer.write(JsNull);
   }
 
   // The magic constant has no meaning. It is just a random value.
   int get hashCode => 785965825;
   DartString toDartString() => const LiteralDartString("null");
 
   accept(ConstantVisitor visitor) => visitor.visitNull(this);
 }
 
 abstract class NumConstant extends PrimitiveConstant {
@@ skipping 347 matching lines @@
     for (int i = 0; i < fields.length; i++) {
       if (fields[i] != other.fields[i]) return false;
     }
     return true;
   }
 
   List<Constant> getDependencies() => fields;
 
   accept(ConstantVisitor visitor) => visitor.visitConstructed(this);
 }