DevTools: Hide the console gap elements from the accessibility tree

Change-Id: Ib3b65c377de9b6fed273bbf6d41daf7d6f275f66
Reviewed-on: https://chromium-review.googlesource.com/1188878Reviewed-by: Andrey Lushnikov <lushnikov@chromium.org>
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586047}

third_party/blink/renderer/devtools/front_end/console/ConsoleViewport.js

@@ -51,6 +51,9 @@ Console.ConsoleViewport = class {
     this._topGapElement.textContent = '\uFEFF';
     this._bottomGapElement.textContent = '\uFEFF';
 
+    UI.ARIAUtils.markAsHidden(this._topGapElement);
+    UI.ARIAUtils.markAsHidden(this._bottomGapElement);
+
     this._provider = provider;
     this.element.addEventListener('scroll', this._onScroll.bind(this), false);
     this.element.addEventListener('copy', this._onCopy.bind(this), false);