Add r/w opt-in rollout flag for RenderEngine on Graphite

This flag will allow some devices to opt in to RE-Graphite as a preview
rollout progresses. Making it a R/W flag will allow for A/B comparison.

Test: manual validation of aconfig flag / sysprop combos
Bug: b/293371537
Flag: com.android.graphics.surfaceflinger.flags.graphite_renderengine_preview_rollout
Change-Id: I30a59986d1da2dc8355c2b3cf2da436c6cc64120
diff --git a/services/surfaceflinger/surfaceflinger_flags_new.aconfig b/services/surfaceflinger/surfaceflinger_flags_new.aconfig
index 34a935a..2c44e4c 100644
--- a/services/surfaceflinger/surfaceflinger_flags_new.aconfig
+++ b/services/surfaceflinger/surfaceflinger_flags_new.aconfig
@@ -173,6 +173,13 @@
 } # frame_rate_category_mrr
 
 flag {
+  name: "graphite_renderengine_preview_rollout"
+  namespace: "core_graphics"
+  description: "R/W flag to enable Skia's Graphite Vulkan backend in RenderEngine, IF it is already compiled with force_compile_graphite_renderengine, AND the debug.renderengine.graphite_preview_optin sysprop is set to true."
+  bug: "293371537"
+} # graphite_renderengine_preview_rollout
+
+flag {
   name: "latch_unsignaled_with_auto_refresh_changed"
   namespace: "core_graphics"
   description: "Ignore eAutoRefreshChanged with latch unsignaled"