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

This CL was uploaded by git cl split.

R=tedchoc@chromium.org

Bug: 1110266
Change-Id: I7149d343729a0970bf5fbcd3bc3a254d5bb30271
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2371220
Auto-Submit: Sean McAllister <smcallis@google.com>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Ted Choc <tedchoc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801088}

chrome/browser/chrome_browser_main.cc

@@ -924,7 +924,7 @@ int ChromeBrowserMainParts::PreCreateThreadsImpl() {
       AddFirstRunNewTabs(browser_creator_.get(), master_prefs_->new_tabs);
     }
 
-#if defined(OS_MAC) || defined(OS_LINUX)
+#if defined(OS_MAC) || defined(OS_LINUX) || defined(OS_CHROMEOS)
     // Create directory for user-level Native Messaging manifest files. This
     // makes it less likely that the directory will be created by third-party
     // software with incorrect owner or permission. See crbug.com/725513 .
@@ -933,7 +933,7 @@ int ChromeBrowserMainParts::PreCreateThreadsImpl() {
                                  &user_native_messaging_dir));
     if (!base::PathExists(user_native_messaging_dir))
       base::CreateDirectory(user_native_messaging_dir);
-#endif  // defined(OS_MAC) || defined(OS_LINUX)
+#endif  // defined(OS_MAC) || defined(OS_LINUX) || defined(OS_CHROMEOS)
   }
 #endif  // !defined(OS_ANDROID) && !defined(OS_CHROMEOS)