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/ui/blocked_content

This CL was uploaded by git cl split.

R=csharrison@chromium.org

Bug: 1110266
Change-Id: I3aa4df135631af02b22232f4a1c9cdbd360c67cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371259
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801133}

chrome/browser/ui/blocked_content/popup_blocker_browsertest.cc

@@ -555,7 +555,7 @@ IN_PROC_BROWSER_TEST_F(PopupBlockerBrowserTest,
 // https://codereview.chromium.org/23903056
 // BUG=https://code.google.com/p/chromium/issues/detail?id=295299
 // TODO(ananta). Debug and fix this test.
-#if defined(USE_AURA) && defined(OS_LINUX)
+#if defined(USE_AURA) && (defined(OS_LINUX) || defined(OS_CHROMEOS))
 #define MAYBE_WindowFeatures DISABLED_WindowFeatures
 #else
 #define MAYBE_WindowFeatures WindowFeatures