Added library comment and warning message to web_sql.

tools/dom/templates/html/dartium/web_sql_dartium.darttemplate

Index: tools/dom/templates/html/dartium/web_sql_dartium.darttemplate
diff --git a/tools/dom/templates/html/dartium/web_sql_dartium.darttemplate b/tools/dom/templates/html/dartium/web_sql_dartium.darttemplate
index 0556070640ee18ea4bb4a76d2b5404e405c82827..2cee355a8131dda5704fc0e0b7b18452569a9a9c 100644
--- a/tools/dom/templates/html/dartium/web_sql_dartium.darttemplate
+++ b/tools/dom/templates/html/dartium/web_sql_dartium.darttemplate
@@ -2,6 +2,17 @@
 // https://code.google.com/p/dart/wiki/ContributingHTMLDocumentation
 // Auto-generated dart:audio library.
 
+/**
+ * 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+ * **Caution:** this specification is no longer actively maintained by the Web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';