Bug 1481549: Configure changes to enable the launcher process by default; r=froydnj

In order to start Firefox via the launcher process, we currently need to pass a
command-line flag. If we are to eventually ship the launcher by default, we want
to be able to configure the build such that the launcher process is used by
default, without any special flags.

This patch simply adds the configure option and sets the config and defines
appropriately.

--HG--
extra : rebase_source : 08847b77a8ff06314a329ae3f4ab9b7046354b30

toolkit/moz.configure

@@ -1048,3 +1048,19 @@ def unsigned_addon_scopes(scopes):
 
 set_config('MOZ_UNSIGNED_APP_SCOPE', unsigned_addon_scopes.app)
 set_config('MOZ_UNSIGNED_SYSTEM_SCOPE', unsigned_addon_scopes.system)
+
+# Launcher process (Windows only)
+# ==============================================================
+
+option('--enable-launcher-process', help='Enable launcher process by default')
+
+@depends('--enable-launcher-process', target)
+def launcher(value, target):
+    enabled = bool(value)
+    if enabled and target.os != 'WINNT':
+        die('Cannot enable launcher process on %s', target.os)
+    if enabled:
+        return True
+
+set_config('MOZ_LAUNCHER_PROCESS', launcher)
+set_define('MOZ_LAUNCHER_PROCESS', launcher)