Fix warnings spotted by dart.

dart/sdk/lib/_internal/compiler/implementation/js_backend/namer.dart

 // Copyright (c) 2011, 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 js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class Namer implements ClosureNamer {
@@ skipping 305 matching lines @@
       ConstructorBodyElement bodyElement = element;
       name = bodyElement.constructor.name;
     }
     FunctionSignature signature = element.computeSignature(compiler);
     String methodName =
         '${privateName(library, name)}\$${signature.parameterCount}';
     if (signature.optionalParametersAreNamed &&
         !signature.optionalParameters.isEmpty) {
       StringBuffer buffer = new StringBuffer();
       signature.orderedOptionalParameters.forEach((Element element) {
-        buffer.add('\$${safeName(element.name.slowToString())}');
+        buffer.write('\$${safeName(element.name.slowToString())}');
       });
       methodName = '$methodName$buffer';
     }
     if (name == closureInvocationSelectorName) return methodName;
     return getMappedInstanceName(methodName);
   }
 
   String publicInstanceMethodNameByArity(SourceString name, int arity) {
     SourceString newName = operatorNameToIdentifier(name);
     if (newName != name) return getMappedOperatorName(newName.slowToString());
@@ skipping 18 matching lines @@
       SourceString name = selector.name;
       if (selector.kind == SelectorKind.OPERATOR
           || selector.kind == SelectorKind.INDEX) {
         name = operatorNameToIdentifier(name);
         assert(name != selector.name);
         return getMappedOperatorName(name.slowToString());
       }
       assert(name == operatorNameToIdentifier(name));
       StringBuffer buffer = new StringBuffer();
       for (SourceString argumentName in selector.getOrderedNamedArguments()) {
-        buffer.add(r'$');
+        buffer.write(r'$');
         argumentName.printOn(buffer);
       }
       String suffix = '\$${selector.argumentCount}$buffer';
       // We don't mangle the closure invoking function name because it
       // is generated by string concatenation in applyFunction from
       // js_helper.dart.
       if (selector.isClosureCall()) {
         return "${name.slowToString()}$suffix";
       } else {
         String proposedName = privateName(selector.library, name);
@@ skipping 165 matching lines @@
       return getName(element);
     }
     // Use the unminified names here to construct the interceptor names.  This
     // helps ensure that they don't all suddenly change names due to a name
     // clash in the minifier, which would affect the diff size.  Sort the names
     // of the classes to ensure name is stable and predicatble for the suggested
     // names.
     StringBuffer buffer = new StringBuffer('${element.name.slowToString()}\$');
     List<String> names = classes.map((cls) => cls.name.slowToString()).toList();
     names.sort();
-    names.forEach(buffer.add);
+    names.forEach(buffer.write);
     return getMappedGlobalName(buffer.toString());
   }
 
   String getBailoutName(Element element) {
     String name = bailoutNames[element];
     if (name != null) return name;
     bool global = !element.isInstanceMember();
     // Despite the name of the variable, this gets the minified name when we
     // are minifying, but it doesn't really make much difference.  The
     // important thing is that it is a unique name.  We add $bailout and, if we
@@ skipping 194 matching lines @@
       return const SourceString(r'$or');
     } else if (value == '-') {
       return const SourceString(r'$sub');
     } else if (value == 'unary-') {
       return const SourceString(r'$negate');
     } else {
       return name;
     }
   }
 }