Use process_singleton_linux on Mac.

chrome/app/chromium_strings.grd

Index: chrome/app/chromium_strings.grd
diff --git a/chrome/app/chromium_strings.grd b/chrome/app/chromium_strings.grd
index a7d38917bb8cb82b1843af58632fab9a1c4c6e55..93feb318303372fb78950c2fb6bed6a73e61fb71 100644
--- a/chrome/app/chromium_strings.grd
+++ b/chrome/app/chromium_strings.grd
@@ -1115,8 +1115,8 @@ Signing in anyway will merge Chromium information like bookmarks, history, and o
       </message>
 
       <!-- ProcessSingleton -->
-      <if expr="is_linux">
-        <message name="IDS_PROFILE_IN_USE_LINUX" desc="Message shown when the browser cannot start because the profile is in use on a different host.">
+      <if expr="is_posix">

[tapted, 2014/04/08 17:56:44]

This might put an unnecessary string in the android resource bundle (and I think
there's a script someone runs checking this..) - maybe is_linux or is_macosx?

[jackhou1, 2014/04/14 04:12:10]

Done.

+        <message name="IDS_PROFILE_IN_USE_POSIX" desc="Message shown when the browser cannot start because the profile is in use on a different host.">
           The profile appears to be in use by another Chromium process (<ph name="PROCESS_ID">$1<ex>12345</ex></ph>) on another computer (<ph name="HOST_NAME">$2<ex>example.com</ex></ph>). Chromium has locked the profile so that it doesn't get corrupted. If you are sure no other processes are using this profile, you can unlock the profile and relaunch Chromium.
         </message>
       </if>
@@ -1184,7 +1184,7 @@ Signing in anyway will merge Chromium information like bookmarks, history, and o
       <message name="IDS_EXTENSIONS_SETTINGS_API_SECOND_LINE_START_AND_SEARCH" desc="Second line in the Settings API bubble. Only shown if the secondary change by the extension was both the start page and the search engine. See IDS_EXTENSIONS_SETTINGS_API_SECOND_LINE_START_PAGES for reason for triple quotes.">
         ''' It also controls what page is shown when you start Chromium or search from the Omnibox. '''
       </message>
-      
+
       <!-- Update bubble -->
       <message name="IDS_REINSTALL_APP" desc="Text for the button the user clicks to reinstall the app.">
         Reinstall Chromium