fbc9537952
The current `flattenSummaries` function re-process the same NgModule summary even if it has been processed before. Certain modules like CommonModule are repeated multiple times in the module tree and it is expanded out every time. This was making unit tests using AOT summaries really slow. This will also slow down JIT bootstrap applications that load AOT summaries for component libraries. The fix is to remember which summaries were seen before and not to process them again.