Only use default strings.xml file as overlayable

If we reference all strings.xml files and then remove a string, the
resource will still be present in our overlayable.xml file. Then, when
translations are imported and the additional references are removed, the
application will no longer build.

Bug: 187225456
Test: manual (on CarSettings)
Change-Id: I114b1fd37cac6d50571bd5173e0bab601db87698
diff --git a/tools/rro/resource_utils.py b/tools/rro/resource_utils.py
index 5e860f9..aae73a1 100644
--- a/tools/rro/resource_utils.py
+++ b/tools/rro/resource_utils.py
@@ -75,7 +75,8 @@
         for file in os.listdir(os.path.join(resDir, dir)):
             filePath = os.path.abspath(os.path.join(resDir, dir, file))
             if file.endswith('.xml') and filePath not in excluded_resource_files:
-                for resource in get_resources_from_single_file(os.path.join(resDir, dir, file)):
+                for resource in get_resources_from_single_file(os.path.join(resDir, dir, file),
+                                                               dir != "values"):
                     add_resource_to_set(resources, resource)
     return resources
 
@@ -87,7 +88,7 @@
             add_resource_to_set(result, Resource(i, 'id', ResourceLocation(filename)))
     return result
 
-def get_resources_from_single_file(filename):
+def get_resources_from_single_file(filename, ignore_strings=False):
     doc = etree.parse(filename)
     root = doc.getroot()
     result = set()
@@ -100,6 +101,8 @@
             resType = "array"
         if resource.tag == 'item' or resource.tag == 'public':
             resType = resource.get('type')
+        if resType == 'string' and ignore_strings:
+            continue
         if resType == 'overlayable':
             for policy in resource:
                 for overlayable in policy: