Disable VerifySiteInstanceCountInBrowsingInstance test.

The test started flaking after an unrelated CL caused a slight change to the
sharding of tests. This implies that the test has previously relied on state
carried over from previous tests to function correctly.

Bug: 934900
Change-Id: Iee0208c99751362a3c5dcf36f70a1625e3ebd6a3
Reviewed-on: https://chromium-review.googlesource.com/c/1483940Reviewed-by: Charlie Reis <creis@chromium.org>
Commit-Queue: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#634858}

chrome/browser/site_details_browsertest.cc

@@ -1047,8 +1047,10 @@ IN_PROC_BROWSER_TEST_F(SiteDetailsBrowserTest,
 
 // Verifies that the UMA counter for SiteInstances in a BrowsingInstance is
 // correct when using tabs with web pages.
+//
+// Disabled since it's flaky. https://crbug.com/934900
 IN_PROC_BROWSER_TEST_F(SiteDetailsBrowserTest,
-                       VerifySiteInstanceCountInBrowsingInstance) {
+                       DISABLED_VerifySiteInstanceCountInBrowsingInstance) {
   // Page with 14 nested oopifs across 9 sites (a.com through i.com).
   GURL abcdefghi_url = embedded_test_server()->GetURL(
       "a.com",