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/metrics/oom

This CL was uploaded by git cl split.

R=csharrison@chromium.org

Bug: 1110266
Change-Id: I09612099e3d071042a3f2765e5976f0b3c001b75
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371252
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@{#801132}

chrome/browser/metrics/oom/out_of_memory_reporter_browsertest.cc

@@ -35,7 +35,8 @@ using ui_test_utils::NavigateToURL;
 
 // No current reliable way to determine OOM on Linux/Mac. Sanitizers also
 // interfere with the exit code on OOM, making this detection unreliable.
-#if defined(OS_LINUX) || defined(OS_MAC) || defined(ADDRESS_SANITIZER)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(OS_MAC) || \
+    defined(ADDRESS_SANITIZER)
 #define MAYBE_OutOfMemoryReporterBrowserTest \
   DISABLED_OutOfMemoryReporterBrowserTest
 #else
@@ -91,7 +92,8 @@ IN_PROC_BROWSER_TEST_F(MAYBE_OutOfMemoryReporterBrowserTest, MemoryExhaust) {
 
 // No current reliable way to determine OOM on Linux/Mac. Sanitizers also
 // interfere with the exit code on OOM, making this detection unreliable.
-#if defined(OS_LINUX) || defined(OS_MAC) || defined(ADDRESS_SANITIZER)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(OS_MAC) || \
+    defined(ADDRESS_SANITIZER)
 #define MAYBE_PortalOutOfMemoryReporterBrowserTest \
   DISABLED_PortalOutOfMemoryReporterBrowserTest
 #else