[Sheriff] MemoryCacheResources_RecordedOncePerContextdisable is flaky

This subtest is currently flaking and I am disabling it (for now).

Bug: 1108534
Change-Id: I7bf50d77a841a87f13b5e1a579d59ed6217dd737
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2314787Reviewed-by: John Delaney <johnidel@chromium.org>
Commit-Queue: Kelvin Jiang <kelvinjiang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791035}

chrome/browser/page_load_metrics/page_load_metrics_browsertest.cc

@@ -2506,8 +2506,9 @@ IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest,
 
 // Verifies that css image resources shared across document do not cause a
 // crash, and are only counted once per context. https://crbug.com/979459.
+// TODO(crbug.com/1108534): Disabled due to flakiness.
 IN_PROC_BROWSER_TEST_F(PageLoadMetricsBrowserTest,
-                       MemoryCacheResources_RecordedOncePerContext) {
+                       DISABLED_MemoryCacheResources_RecordedOncePerContext) {
   embedded_test_server()->ServeFilesFromSourceDirectory("chrome/test/data");
   content::SetupCrossSiteRedirector(embedded_test_server());
   ASSERT_TRUE(embedded_test_server()->Start());