Skip flaky RealtimeCpuChartTest.InitializePlot

TBR=joonbug@chromium.org

Bug: 1139523
Change-Id: I03307649b4d5eb833650d578313e3a37645fe947
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2484024Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Commit-Queue: Alice Boxhall <aboxhall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818354}

chrome/test/data/webui/chromeos/diagnostics/realtime_cpu_chart_test.js

@@ -81,7 +81,8 @@ suite('RealtimeCpuChartTest', () => {
     });
   });
 
-  test('InitializePlot', () => {
+  // Flaky: https://crbug.com/1139523
+  test.skip('InitializePlot', () => {
     const user = 10;
     const system = 30;
     return initializeRealtimeCpuChart(user, system).then(() => {