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 /components/policy

This CL was uploaded by git cl split.

R=zmin@chromium.org

Bug: 1110266
Change-Id: I5f11621031a312f4572006cfbcd8ebf3181dd63f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2370291
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801062}

components/policy/core/common/cloud/cloud_policy_client_unittest.cc

@@ -1505,7 +1505,8 @@ TEST_F(CloudPolicyClientTest, UploadChromeOsUserReport) {
   EXPECT_EQ(DM_STATUS_SUCCESS, client_->status());
 }
 
-#if defined(OS_WIN) || defined(OS_APPLE) || defined(OS_LINUX)
+#if defined(OS_WIN) || defined(OS_APPLE) || defined(OS_LINUX) || \
+    defined(OS_CHROMEOS)
 TEST_F(CloudPolicyClientTest, UploadRealtimeReport) {
   RegisterClient();
 

components/policy/core/common/cloud/cloud_policy_util.cc

@@ -129,7 +129,7 @@ std::string GetMachineName() {
 }
 
 std::string GetOSVersion() {
-#if defined(OS_LINUX) || defined(OS_APPLE)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS) || defined(OS_APPLE)
   return base::SysInfo::OperatingSystemVersion();
 #elif defined(OS_WIN)
   base::win::OSInfo::VersionNumber version_number =