[Android] Fix some linker errors from browser startup.

A step towards actually using BrowserMainPartsAndroid

BUG=138184


Review URL: https://chromiumcodereview.appspot.com/10875019

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@152881 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/chrome/browser/browser_process_impl.cc b/chrome/browser/browser_process_impl.cc
index a2a03ee..42b81c3 100644
--- a/chrome/browser/browser_process_impl.cc
+++ b/chrome/browser/browser_process_impl.cc
@@ -553,9 +553,14 @@
 
 BackgroundModeManager* BrowserProcessImpl::background_mode_manager() {
   DCHECK(CalledOnValidThread());
+#if defined(ENABLE_BACKGROUND)
   if (!background_mode_manager_.get())
     CreateBackgroundModeManager();
   return background_mode_manager_.get();
+#else
+  NOTIMPLEMENTED();
+  return NULL;
+#endif
 }
 
 StatusTray* BrowserProcessImpl::status_tray() {