SF: make RenderEngineThreaded::waitUntilInitialized more efficient

RenderEngineThreaded::waitUntilInitialized is called from multiple
threads. Use atomic to avoid contending on a mutex.

Bug: 313924033
Test: presubmit
(cherry picked from commit 36135d0e0f880d28a77792bd1b7519e3a2110a8d)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d6ac7795876884aa18e565ebdd1400b49acc5c64)
Merged-In: I4d61240a76f3ca814c28ccba62626f8b43a125cd
Change-Id: I4d61240a76f3ca814c28ccba62626f8b43a125cd
2 files changed