Fix AppWindowApiTest.Get#testGetAllMultipleWindows properly

Its comparator was rubbish and always has been. Array.prototype.sort()
takes a function that should return {-1, 0, 1}, not bool.

TBR=benwells@chromium.org

Bug: 877890
Change-Id: I65162d2b261ad4ff91a028bf62c0cdcfb765df27
Reviewed-on: https://chromium-review.googlesource.com/1188736Reviewed-by: Trent Apted <tapted@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586206}

chrome/test/data/extensions/platform_apps/windows_api_get/background.js

@@ -3,7 +3,7 @@
 // found in the LICENSE file.
 
 function compareId(a, b) {
-  return a.id < b.id;
+  return a.id.localeCompare(b.id);
 }
 
 chrome.app.runtime.onLaunched.addListener(function() {