Add permitted_when_isolated_path to linker namespaces

The permitted_when_isolated_path is a way to white-list
directories not present in search-path. It is ignored for
not isolated namespaces.

Bug: http://b/25853516
Bug: http://b/22548808
Change-Id: Ib1538037268eea69323ea49968a34a4a1d1938a5
diff --git a/linker/tests/linker_utils_test.cpp b/linker/tests/linker_utils_test.cpp
index 3be9b3f..fd749fa 100644
--- a/linker/tests/linker_utils_test.cpp
+++ b/linker/tests/linker_utils_test.cpp
@@ -54,6 +54,18 @@
   ASSERT_FALSE(file_is_in_dir("/file", "/"));
 }
 
+TEST(linker_utils, file_is_under_dir_smoke) {
+  ASSERT_TRUE(file_is_under_dir("/foo/bar/file", "/foo/bar"));
+  ASSERT_TRUE(file_is_under_dir("/foo/bar/file", "/foo"));
+
+  ASSERT_FALSE(file_is_under_dir("/foo/bar/file", "/bar/foo"));
+
+  ASSERT_TRUE(file_is_under_dir("/file", ""));
+  ASSERT_TRUE(file_is_under_dir("/foo/bar/file", ""));
+  ASSERT_FALSE(file_is_under_dir("/file", "/"));
+  ASSERT_FALSE(file_is_under_dir("/foo/bar/file", "/"));
+}
+
 TEST(linker_utils, parse_zip_path_smoke) {
   std::string zip_path;
   std::string entry_path;