Document DOMApplicationCache as fix for https://code.google.com/p/dart/issues/detail?id=3688.

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "AbstractWorker": {
       "members": {
         "errorEvent": [
           "/**",
           "   * Static factory designed to expose `error` events to event",
           "   * handlers that are not necessarily instances of [AbstractWorker].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
         "onerror": [
           "/// Stream of `error` events handled by this [AbstractWorker]."
         ]
       }
     },
     "ApplicationCache": {
+      "comment": [
+        "/**",
+        " * ApplicationCache is accessed via [Window.applicationCache].",
+        " */"
+      ],
       "members": {
         "cachedEvent": [
           "/**",
           "   * Static factory designed to expose `cached` events to event",
           "   * handlers that are not necessarily instances of [ApplicationCache].",
           "   *",
           "   * See [EventStreamProvider] for usage information.",
           "   */"
         ],
         "checkingEvent": [
@@ skipping 5233 matching lines @@
           "   *",
           "   * [oldVersion] should match the database's current [version] exactly.",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }