Disabled failing chromevox test.

BackgroundTest.NavigationEscapesEdit fails on linux-chromeos-dbg.

TBR=dtseng@chromium.org

Bug: 872258
Change-Id: I4dc957a290bebb4cfa9d60c0a5240100de111240
Reviewed-on: https://chromium-review.googlesource.com/1167057Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Commit-Queue: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581543}

chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs

@@ -1473,7 +1473,8 @@ TEST_F('BackgroundTest', 'DISABLED_ActiveDescendantUpdates', function() {
   });
 });
 
-TEST_F('BackgroundTest', 'NavigationEscapesEdit', function() {
+// Fails consistently (timeout) on linux-chromeos-dbg https://crbug.com/872258
+TEST_F('BackgroundTest', 'DISABLED_NavigationEscapesEdit', function() {
   var mockFeedback = this.createMockFeedback();
   this.runWithLoadedTree(function() {/*!
     <p>before content editable</p>