Added library comment and warning message to web_sql.

sdk/lib/web_sql/dart2js/web_sql_dart2js.dart

+/**
+ * An API for storing data in the browser that can be queried with SQL.
+ *
+ * **Caution:** this specification is no longer actively maintained by the Web
+ * Applications Working Group and may be removed at any time.
+ * See [the W3C Web SQL Database specification](http://www.w3.org/TR/webdatabase/)
+ * for more information.
+ *
+ * The [dart:html.Storage] or [dart:indexed_db] APIs are recommended
+ * alternatives.
+ */
 library dart.dom.web_sql;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:html';
 import 'dart:html_common';
 import 'dart:_js_helper' show convertDartClosureToJS, Creates, JavaScriptIndexingBehavior, JSName;
 import 'dart:_foreign_helper' show JS;
 // DO NOT EDIT - unless you are editing documentation as per:
 // https://code.google.com/p/dart/wiki/ContributingHTMLDocumentation
@@ skipping 442 matching lines @@
 @DomName('SQLTransactionSync')
 @SupportedBrowser(SupportedBrowser.CHROME)
 @SupportedBrowser(SupportedBrowser.SAFARI)
 @Experimental
 class SqlTransactionSync native "*SQLTransactionSync" {
 
   @DomName('SQLTransactionSync.executeSql')
   @DocsEditable
   SqlResultSet executeSql(String sqlStatement, List arguments) native;
 }