Mark a ScrollLatencyCompositedScrollbarBrowserTest as flaky.

Bug: 1122371
Change-Id: I494aaa813faa6138c40629d567ebc0332a1047de
TBR: dtapuska@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2382068Reviewed-by: Mustaq Ahmed <mustaq@chromium.org>
Commit-Queue: Mustaq Ahmed <mustaq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803959}

content/browser/renderer_host/input/scroll_latency_browsertest.cc

@@ -493,8 +493,9 @@ class ScrollLatencyScrollbarBrowserTest : public ScrollLatencyBrowserTest {
   base::test::ScopedFeatureList scoped_feature_list_;
 };
 
+// This test flakes on most platforms: https://crbug.com/1122371.
 IN_PROC_BROWSER_TEST_F(ScrollLatencyScrollbarBrowserTest,
-                       ScrollbarButtonLatency) {
+                       DISABLED_ScrollbarButtonLatency) {
   LoadURL();
 
   RunScrollbarButtonLatencyTest();