Kaleidoscope: Let JS set toolbar menu button tooltip text

Bug: b:166321735
Change-Id: I53aa13485ac9f014c6ebc0ab8bf38f65204e0637
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2375600Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801817}

chrome/browser/resources/kaleidoscope/toolbar.html

@@ -8,4 +8,4 @@
     z-index: 1;
   }
 </style>
-<cr-toolbar id="toolbar" show-menu show-search="[[showSearch]]"></cr-toolbar>
+<cr-toolbar id="toolbar" show-menu show-search="[[showSearch]]" menu-label="[[menuLabel]]"></cr-toolbar>

chrome/browser/resources/kaleidoscope/toolbar.js

@@ -19,6 +19,9 @@ class KaleidoscopeToolbarElement extends PolymerElement {
     return {
       // Controls whether the search field is shown.
       showSearch: {type: Boolean, value: false},
+
+      // Sets the tooltip text displayed on the menu button.
+      menuLabel: {type: String, value: ''},
     };
   }
 }