Disable SitePerProcessBrowserTest.NestedFrameViewportIntersectionUpdated on Linux

It is flaky.

Bug: 869758
Change-Id: Ic9c29ced0103a11ae284b10d49466fa317c605b2
Tbr: kenrb@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/1215508
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589867}

content/browser/site_per_process_browsertest.cc

@@ -12103,8 +12103,8 @@ IN_PROC_BROWSER_TEST_F(SitePerProcessBrowserTest,
 
 // Test to verify that viewport intersection is propagated to nested OOPIFs
 // even when a parent OOPIF has been throttled.
-// TODO(crbug.com/869758) The test is flaky on android
-#if defined(OS_ANDROID)
+// TODO(crbug.com/869758) The test is flaky on android and Linux.
+#if defined(OS_ANDROID) || defined(OS_LINUX)
 #define MAYBE_NestedFrameViewportIntersectionUpdated \
   DISABLED_NestedFrameViewportIntersectionUpdated
 #else