Add chrome/browser/apps/BUILD.gn and move Chrome-specific code there

apps/saved_files_service.h

Index: apps/saved_files_service.h
diff --git a/apps/saved_files_service.h b/apps/saved_files_service.h
index 0007d660ffa309f75462bcaab773aed723b0f3ca..927f22b985869eccca6f5787920c180b37b34dad 100644
--- a/apps/saved_files_service.h
+++ b/apps/saved_files_service.h
@@ -101,6 +101,9 @@ class SavedFilesService : public KeyedService,
   // Clears all retained files.
   void ClearQueue(const extensions::Extension* extension);
 
+  // Called to notify that the application has begun to exit.
+  void OnApplicationTerminating();
+
  private:
   FRIEND_TEST_ALL_PREFIXES(::SavedFilesServiceUnitTest, RetainTwoFilesTest);
   FRIEND_TEST_ALL_PREFIXES(::SavedFilesServiceUnitTest, EvictionTest);