Disable PreviewsNoScriptBrowserTest.NoScriptPreviewsEnabled on Linux

Because they seem to be flaky on Linux Xenial.

TBR=tbansal

Bug: 869781
Change-Id: I8a396d51256b67e6ef3d5d6e9d4ae4cda365ad1b
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1158120Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579725}

chrome/browser/previews/previews_browsertest.cc

@@ -176,7 +176,8 @@ class PreviewsNoScriptBrowserTest : public PreviewsBrowserTest {
 // Previews InfoBar (which these tests triggers) does not work on Mac.
 // See crbug.com/782322 for detail.
 // Also occasional flakes on win7 (crbug.com/789542).
-#if defined(OS_ANDROID) || defined(OS_LINUX)
+// Also occasional flakes on Linux Xenial (crbug.com/869781).
+#if defined(OS_ANDROID)
 #define MAYBE_NoScriptPreviewsEnabled NoScriptPreviewsEnabled
 #define MAYBE_NoScriptPreviewsEnabledHttpRedirectToHttps \
   NoScriptPreviewsEnabledHttpRedirectToHttps