Generate a boot image extension for mainline BCP jars.

Bug: 269230245
Test: m
Test: atest art_standalone_dexpreopt_tests
Change-Id: I253c30d938eee2cf2549ec2338425d53956e7cbb
diff --git a/java/dexpreopt.go b/java/dexpreopt.go
index e0a0629..0ffedf6 100644
--- a/java/dexpreopt.go
+++ b/java/dexpreopt.go
@@ -293,6 +293,12 @@
 	isSystemServerJar := global.AllSystemServerJars(ctx).ContainsJar(moduleName(ctx))
 
 	bootImage := defaultBootImageConfig(ctx)
+	// When `global.PreoptWithUpdatableBcp` is true, `bcpForDexpreopt` below includes the mainline
+	// boot jars into bootclasspath, so we should include the mainline boot image as well because it's
+	// generated from those jars.
+	if global.PreoptWithUpdatableBcp {
+		bootImage = mainlineBootImageConfig(ctx)
+	}
 	dexFiles, dexLocations := bcpForDexpreopt(ctx, global.PreoptWithUpdatableBcp)
 
 	targets := ctx.MultiTargets()