Refactor OS_LINUX preprocessor directive for LaCrOS effort.

Currently, ChromeOS defines the OS_LINUX directive as well as
OS_CHROMEOS.  We're working to separate these two, so we're
making the fact that OS_LINUX == OS_LINUX || OS_CHROMEOS
explicit.

This is changes for /chrome/browser/media/media_engagement_browsertest.cc

This CL was uploaded by git cl split.

R=beccahughes@chromium.org

Bug: 1110266
Change-Id: Ic8150752c7c605d957c4516914586543fc310001
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371247
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801018}

chrome/browser/media/media_engagement_browsertest.cc

@@ -525,7 +525,7 @@ IN_PROC_BROWSER_TEST_F(MediaEngagementBrowserTest,
   ExpectScores(1, 0);
 }
 
-#if defined(OS_WIN) || defined(OS_LINUX)
+#if defined(OS_WIN) || defined(OS_LINUX) || defined(OS_CHROMEOS)
 // Flaky: https://crbug.com/1115238
 #define MAYBE_RecordVisitOnNewOrigin DISABLED_RecordVisitOnNewOrigin
 #else