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/extensions/api/notifications

This CL was uploaded by git cl split.

R=dewittj@chromium.org

Bug: 1110266
Change-Id: I439c0eb3fb6b5bd32a591f904c49430cf4d6825c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371242Reviewed-by: Justin DeWitt <dewittj@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Cr-Commit-Position: refs/heads/master@{#801264}

chrome/browser/extensions/api/notifications/notifications_apitest.cc

@@ -222,7 +222,8 @@ class NotificationsApiTest : public extensions::ExtensionApiTest {
 }  // namespace
 
 // http://crbug.com/691913
-#if (defined(OS_LINUX) || defined(OS_WIN)) && !defined(NDEBUG)
+#if (defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(OS_WIN)) && \
+    !defined(NDEBUG)
 #define MAYBE_TestBasicUsage DISABLED_TestBasicUsage
 #else
 #define MAYBE_TestBasicUsage TestBasicUsage