MD Bookmarks: Update a couple of TODOs

This completes one TODO (adding an error message to StoreClient),
and removes another obsolete TODO.

BUG=697706
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2858483002
Cr-Commit-Position: refs/heads/master@{#468574}

chrome/browser/resources/md_bookmarks/store_client.js

@@ -49,7 +49,10 @@ cr.define('bookmarks', function() {
      * @param {function(!BookmarksPageState)} valueGetter
      */
     watch: function(localProperty, valueGetter) {
-      // TODO(tsergeant): Warn if localProperty is not a defined property.
+      if (!this.getPropertyInfo(localProperty).defined) {
+        console.error(
+            'No property ' + localProperty + ' defined on ' + this.is);
+      }
       this.watches_.push({
         localProperty: localProperty,
         valueGetter: valueGetter,

chrome/test/data/webui/md_bookmarks/test_store.js

@@ -52,11 +52,13 @@ suiteSetup(function() {
           bookmarks.Store.prototype.reduce_.call(this, action);
       },
 
+      /**
+       * Notifies UI elements that the store data has changed. When reducers are
+       * disabled, tests are responsible for manually changing the data to make
+       * UI elements update correctly (eg, tests must replace the whole list
+       * when changing a single element).
+       */
       notifyObservers: function() {
-        // TODO(tsergeant): Revisit how state modifications work in UI tests.
-        // We don't want tests to worry about modifying the whole state tree.
-        // Instead, we could perform a deep clone in here to ensure that every
-        // StoreClient is updated.
         this.notifyObservers_(this.data);
       },