Fix deprecation warnings in dart:io. Now completely warning free.

sdk/lib/io/http_headers.dart

 // Copyright (c) 2013, 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 dart.io;
 
 class _HttpHeaders implements HttpHeaders {
   _HttpHeaders(String this.protocolVersion)
       : _headers = new Map<String, List<String>>();
 
@@ skipping 377 matching lines @@
       }
       buffer[bufferPos++] = _CharCode.CR;
       buffer[bufferPos++] = _CharCode.LF;
     });
     writeBuffer();
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     _headers.forEach((String name, List<String> values) {
-      sb.add(name);
-      sb.add(": ");
+      sb.write(name);
+      sb.write(": ");
       bool fold = _foldHeader(name);
       for (int i = 0; i < values.length; i++) {
         if (i > 0) {
           if (fold) {
-            sb.add(", ");
+            sb.write(", ");
           } else {
-            sb.add("\n");
-            sb.add(name);
-            sb.add(": ");
+            sb.write("\n");
+            sb.write(name);
+            sb.write(": ");
           }
         }
-        sb.add(values[i]);
+        sb.write(values[i]);
       }
-      sb.add("\n");
+      sb.write("\n");
     });
     return sb.toString();
   }
 
   List<Cookie> _parseCookies() {
     // Parse a Cookie header value according to the rules in RFC 6265.
     var cookies = new List<Cookie>();
     void parseCookieString(String s) {
       int index = 0;
 
@@ skipping 76 matching lines @@
     _parse(value);
   }
 
   Map<String, String> get parameters {
     if (_parameters == null) _parameters = new Map<String, String>();
     return _parameters;
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
-    sb.add(value);
+    sb.write(value);
     if (parameters != null && parameters.length > 0) {
       _parameters.forEach((String name, String value) {
-        sb.add("; ");
-        sb.add(name);
-        sb.add("=");
-        sb.add(value);
+        sb.write("; ");
+        sb.write(name);
+        sb.write("=");
+        sb.write(value);
       });
     }
     return sb.toString();
   }
 
   void _parse(String s) {
     int index = 0;
 
     bool done() => index == s.length;
 
@@ skipping 46 matching lines @@
           while (!done()) {
             if (s[index] == "\\") {
               if (index + 1 == s.length) {
                 throw new HttpException("Failed to parse header value");
               }
               index++;
             } else if (s[index] == "\"") {
               index++;
               break;
             }
-            sb.add(s[index]);
+            sb.write(s[index]);
             index++;
           }
           return sb.toString();
         } else {
           // Parse non-quoted value.
           return parseValue();
         }
       }
 
       while (!done()) {
@@ skipping 156 matching lines @@
     }
     index++;  // Skip the = character.
     value = parseValue();
     if (done()) return;
     index++;  // Skip the ; character.
     parseAttributes();
   }
 
   String toString() {
     StringBuffer sb = new StringBuffer();
-    sb.add(name);
-    sb.add("=");
-    sb.add(value);
+    sb.write(name);
+    sb.write("=");
+    sb.write(value);
     if (expires != null) {
-      sb.add("; Expires=");
-      sb.add(_HttpUtils.formatDate(expires));
+      sb.write("; Expires=");
+      sb.write(_HttpUtils.formatDate(expires));
     }
     if (maxAge != null) {
-      sb.add("; Max-Age=");
-      sb.add(maxAge);
+      sb.write("; Max-Age=");
+      sb.write(maxAge);
     }
     if (domain != null) {
-      sb.add("; Domain=");
-      sb.add(domain);
+      sb.write("; Domain=");
+      sb.write(domain);
     }
     if (path != null) {
-      sb.add("; Path=");
-      sb.add(path);
+      sb.write("; Path=");
+      sb.write(path);
     }
-    if (secure) sb.add("; Secure");
-    if (httpOnly) sb.add("; HttpOnly");
+    if (secure) sb.write("; Secure");
+    if (httpOnly) sb.write("; HttpOnly");
     return sb.toString();
   }
 
   String name;
   String value;
   DateTime expires;
   int maxAge;
   String domain;
   String path;
   bool httpOnly = false;
   bool secure = false;
 }