Page rendering not cancelled exception in renderPage

- Fix concurrency issue in renderPage using synchronization
- Avoid race condition in renderPage by updating callback instead of throwing exception

Test: N/A (manual test)
Bug: 344104578
Flag: EXEMPT No automated test available for this concurrency fix
Change-Id: I5c8f34eebf830e3c0a131d6fb940b1ef848c3a0d
1 file changed