Fix gn gen with incremental_apk_by_default

Fixes gn gen failing on Android when incremental_apk_by_default is true
due to not forwarding additional_apks for monochrome_public_test_ar_apk.

Bug: 863102
Change-Id: If2c168e5e966f3464056131635be84ede8f568e3
Reviewed-on: https://chromium-review.googlesource.com/1135911
Commit-Queue: agrieve <agrieve@chromium.org>
Reviewed-by: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574813}

build/config/android/rules.gni

@@ -2810,12 +2810,13 @@ if (enable_java_templates) {
       _incremental_test_name = "${invoker.target_name}_incremental"
     }
 
-    if (incremental_apk_by_default) {
+    if (incremental_apk_by_default && _incremental_allowed) {
       _incremental_test_runner_target_name = _test_runner_target_name
       _incremental_test_name = invoker.target_name
     }
 
-    if (!incremental_apk_by_default) {
+    if (!incremental_apk_by_default ||
+        (incremental_apk_by_default && !_incremental_allowed)) {
       test_runner_script(_test_runner_target_name) {
         forward_variables_from(invoker,
                                [
@@ -2901,7 +2902,7 @@ if (enable_java_templates) {
     }
 
     group(target_name) {
-      if (incremental_apk_by_default) {
+      if (incremental_apk_by_default && _incremental_allowed) {
         public_deps = [
           ":${target_name}_incremental",
         ]