Expand OS_LINUX to OS_LINUX || OS_CHROMEOS.

Currently OS_LINUX is defined on Chrome OS Build,
but it will be unset. This is the preparation to keep
the current behavior.

Bug: 1110266
Test: Built locally.
Change-Id: I15f8a6f70c0f3ed17cbad78fd8dd7ddd71c31847
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2449611
Auto-Submit: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: ssid <ssid@chromium.org>
Commit-Queue: Hidehiko Abe <hidehiko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814015}

services/resource_coordinator/public/cpp/memory_instrumentation/tracing_observer_proto_unittest.cc

@@ -127,7 +127,7 @@ memory_instrumentation::mojom::OSMemDump GetFakeOSMemDump(
   return memory_instrumentation::mojom::OSMemDump(
       resident_set_kb, /*peak_resident_set_kb=*/resident_set_kb,
       /*is_peak_rss_resettable=*/true, private_footprint_kb, shared_footprint_kb
-#if defined(OS_LINUX) || defined(OS_ANDROID)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(OS_ANDROID)
       ,
       0
 #endif