[Sheriff] Disable flaky NewTabPageCustomizeDialogTest.All

This test is flaky:
[FATAL:web_contents_observer_sanity_checker.cc(318)] Check failed: !is_loading_.

Example failure: https://ci.chromium.org/p/chromium/builders/ci/Win7%20Tests%20%28dbg%29%281%29/81768

TBR=aee

Bug: 1056688
Change-Id: I5b6d229ea2178bb2f6ee35e7af5b3423f2f6ad66
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2079031Reviewed-by: Katie Dektar <katie@chromium.org>
Commit-Queue: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745128}

chrome/test/data/webui/new_tab_page/new_tab_page_browsertest.js

@@ -60,7 +60,8 @@ var NewTabPageCustomizeDialogTest = class extends NewTabPageBrowserTest {
   }
 };
 
-TEST_F('NewTabPageCustomizeDialogTest', 'All', function() {
+// Test is flaky: crbug.com/1056688.
+TEST_F('NewTabPageCustomizeDialogTest', 'DISABLED_All', function() {
   mocha.run();
 });