Disable BookmarkBarViewTest17.ContextMenus3 as it's flaky.

I see it sometimes failing on try jobs even with reruns. i.e.
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_swarming/builds/1619
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_swarming/builds/1672

BUG=128961
TBR=sky@chromium.org

Review URL: https://codereview.chromium.org/473733004

Cr-Commit-Position: refs/heads/master@{#289638}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289638 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/views/bookmarks/bookmark_bar_view_test.cc

@@ -1685,6 +1685,8 @@ class BookmarkBarViewTest17 : public BookmarkBarViewEventTestBase {
 #elif defined(USE_OZONE)
 // ozone bringup - http://crbug.com/401304
 #define MAYBE_ContextMenus3 DISABLED_ContextMenus3
+#elif defined(OS_WIN)  // http://crbug.com/128961
+#define MAYBE_ContextMenus3 DISABLED_ContextMenus3
 #else
 #define MAYBE_ContextMenus3 ContextMenus3
 #endif