APEX certificates can be overriden by PRODUCT_CERTIFICATE_OVERRIDES

Test: m (apex_test amended)
Change-Id: I9b66a250c9ca20ad754e12455de2b444cf19b1fa

apex/apex.go

@@ -517,12 +517,20 @@ func (a *apexBundle) DepsMutator(ctx android.BottomUpMutatorContext) {
 	}
 	ctx.AddDependency(ctx.Module(), keyTag, String(a.properties.Key))
 
-	cert := android.SrcIsModule(String(a.properties.Certificate))
+	cert := android.SrcIsModule(a.getCertString(ctx))
 	if cert != "" {
 		ctx.AddDependency(ctx.Module(), certificateTag, cert)
 	}
 }
 
+func (a *apexBundle) getCertString(ctx android.BaseContext) string {
+	certificate, overridden := ctx.DeviceConfig().OverrideCertificateFor(ctx.ModuleName())
+	if overridden {
+		return ":" + certificate
+	}
+	return String(a.properties.Certificate)
+}
+
 func (a *apexBundle) Srcs() android.Paths {
 	if file, ok := a.outputFiles[imageApex]; ok {
 		return android.Paths{file}