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/updater

This CL was uploaded by git cl split.

R=sorin@chromium.org

Bug: 1110266
Change-Id: Ic96765ed15e30fdc5c6c84804c75f4290dcefc8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2370289Reviewed-by: Sorin Jianu <sorin@chromium.org>
Commit-Queue: Sean McAllister <smcallis@google.com>
Cr-Commit-Position: refs/heads/master@{#803125}

chrome/updater/installer.cc

@@ -244,12 +244,12 @@ base::FilePath Installer::GetCurrentInstallDir() const {
   return GetAppInstallDir(app_id_).AppendASCII(pv_.GetString());
 }
 
-#if defined(OS_LINUX)
+#if defined(OS_LINUX) || defined(OS_CHROMEOS)
 int Installer::RunApplicationInstaller(const base::FilePath& app_installer,
                                        const std::string& arguments) {
   NOTREACHED();
   return -1;
 }
-#endif  // OS_LINUX
+#endif  // defined(OS_LINUX) || defined(OS_CHROMEOS)
 
 }  // namespace updater