Fix warnings spotted by dart.

dart/sdk/lib/_internal/compiler/implementation/js_backend/emitter.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 js_backend;
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
@@ skipping 1332 matching lines @@
     /* Do nothing. */
   }
 
   void emitClassFields(ClassElement classElement,
                        ClassBuilder builder,
                        { String superClass: "",
                          bool classIsNative: false}) {
     bool isFirstField = true;
     StringBuffer buffer = new StringBuffer();
     if (!classIsNative) {
-      buffer.add('$superClass;');
+      buffer.write('$superClass;');
     }
     visitClassFields(classElement, (Element member,
                                     String name,
                                     String accessorName,
                                     bool needsGetter,
                                     bool needsSetter,
                                     bool needsCheckedSetter) {
       // Ignore needsCheckedSetter - that is handled below.
       bool needsAccessor = (needsGetter || needsSetter);
       // We need to output the fields for non-native classes so we can auto-
       // generate the constructor.  For native classes there are no
       // constructors, so we don't need the fields unless we are generating
       // accessors at runtime.
       if (!classIsNative || needsAccessor) {
         // Emit correct commas.
         if (isFirstField) {
           isFirstField = false;
         } else {
-          buffer.add(',');
+          buffer.write(',');
         }
         int flag = 0;
         if (!needsAccessor) {
           // Emit field for constructor generation.
           assert(!classIsNative);
-          buffer.add(name);
+          buffer.write(name);
         } else {
           // Emit (possibly renaming) field name so we can add accessors at
           // runtime.
-          buffer.add(accessorName);
+          buffer.write(accessorName);
           if (name != accessorName) {
-            buffer.add(':$name');
+            buffer.write(':$name');
             // Only the native classes can have renaming accessors.
             assert(classIsNative);
             flag = RENAMING_FLAG;
           }
         }
         if (needsGetter && needsSetter) {
-          buffer.addCharCode(GETTER_SETTER_CODE + flag);
+          buffer.writeCharCode(GETTER_SETTER_CODE + flag);
         } else if (needsGetter) {
-          buffer.addCharCode(GETTER_CODE + flag);
+          buffer.writeCharCode(GETTER_CODE + flag);
         } else if (needsSetter) {
-          buffer.addCharCode(SETTER_CODE + flag);
+          buffer.writeCharCode(SETTER_CODE + flag);
         }
       }
     });
 
     String compactClassData = buffer.toString();
     if (compactClassData.length > 0) {
       builder.addProperty('', js.string(compactClassData));
     }
   }
 
@@ skipping 1270 matching lines @@
 """;
 const String HOOKS_API_USAGE = """
 // The code supports the following hooks:
 // dartPrint(message)   - if this function is defined it is called
 //                        instead of the Dart [print] method.
 // dartMainRunner(main) - if this function is defined, the Dart [main]
 //                        method will not be invoked directly.
 //                        Instead, a closure that will invoke [main] is
 //                        passed to [dartMainRunner].
 """;