Disable more flaky ChromeVoxLiveRegionsUnitTests.

ChromeVoxLiveRegionsUnitTest.RevealAlertLiveRegion
ChromeVoxLiveRegionsUnitTest.ProgressBarLiveRegionEvents

R=dmazzoni@chromium.org
TBR=dmazzoni
NOTRY=true

Change-Id: If0e8d93719f448f8b014a7d9de33d3d764734954
Bug: 498881
Reviewed-on: https://chromium-review.googlesource.com/c/1355990
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612419}

chrome/browser/resources/chromeos/chromevox/chromevox/injected/live_regions_test.unitjs

@@ -70,7 +70,8 @@ TEST_F('ChromeVoxLiveRegionsUnitTest', 'DISABLED_InsertAlertLiveRegion',
  * Test making text appear inside an 'alert' live region by setting its
  * display to something other than 'none'.
  */
-TEST_F('ChromeVoxLiveRegionsUnitTest', 'RevealAlertLiveRegion', function() {
+// Flaky on Chromium OS: crbug.com/498881.
+TEST_F('ChromeVoxLiveRegionsUnitTest', 'DISABLED_RevealAlertLiveRegion', function() {
   this.loadDoc(function() {/*!
     <div role="alert">
       <style>
@@ -189,7 +190,8 @@ TEST_F('ChromeVoxLiveRegionsUnitTest', 'DISABLED_RemoveFromLiveRegion', function
 /**
  * Test live region that's a progress bar through the event watcher.
  */
-TEST_F('ChromeVoxLiveRegionsUnitTest', 'ProgressBarLiveRegionEvents', function() {
+// Flaky on Chromium OS: crbug.com/498881.
+TEST_F('ChromeVoxLiveRegionsUnitTest', 'DISABLED_ProgressBarLiveRegionEvents', function() {
   this.loadDoc(function() {/*!
     <div id="progress" role="progressbar" aria-live="polite" aria-valuenow="1">
       <div id="ptext">