Fix docs_test. I just learned that when updating docs under html we also need to

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "CanvasGradient": {
       "comment": [
         "/**",
         " * An opaque canvas object representing a gradient.",
         " *",
         " * Created by calling [createLinearGradient] or [createRadialGradient] on a",
         " * [CanvasRenderingContext2D] object.",
         " *",
@@ skipping 170 matching lines @@
           "/// The height of this canvas element in CSS pixels."
         ],
         "width": [
           "/// The width of this canvas element in CSS pixels."
         ]
       }
     },
     "HTMLDivElement": {
       "comment": [
         "/**",
-        " * Represents an HTML <div> element.",
+        " * A generic container for content on an HTML page;",
+        " * corresponds to the &lt;div&gt; tag.",
         " *",
-        " * The [DivElement] is a generic container for content and does not have any",
-        " * special significance. It is functionally similar to [SpanElement].",
+        " * The [DivElement] is a generic container and does not have any semantic",
+        " * significance. It is functionally similar to [SpanElement].",
         " *",
         " * The [DivElement] is a block-level element, as opposed to [SpanElement],",
         " * which is an inline-level element.",
         " *",
         " * Example usage:",
         " *",
         " *     DivElement div = new DivElement();",
         " *     div.text = 'Here's my new DivElem",
         " *     document.body.elements.add(elem);",
         " *",
@@ skipping 267 matching lines @@
           "   *",
           "   * is the (more verbose) equivalent of",
           "   *",
           "   *     HttpRequest.getString('http://dartlang.org').then(",
           "   *         (result) => print('Request complete: $result'));",
           "   */"
         ]
       }
     }
   },
+  "dart.dom.indexed_db": {
+    "IDBDatabase": {
+      "comment": [
+        "/**",
+        " * An indexed database object for storing client-side data",
+        " * in web apps.",
+        " */"
+      ]
+    }
+  },
   "dart.dom.web_audio": {
     "ScriptProcessorNode": {
       "members": {
         "onaudioprocess": [
           "/**",
           "   * Get a Stream that fires events when AudioProcessingEvents occur.",
           "   * This particular stream is special in that it only allows one listener to a",
           "   * given stream. Converting the returned Stream [asBroadcast] will likely ruin",
           "   * the soft-real-time properties which which these events are fired and can",
           "   * be processed.",
@@ skipping 16 matching lines @@
           "   *",
           "   * [oldVersion] should match the database's current [version] exactly.",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }