Shared namespaces inherit parent ns properties

Make shared namespace inherit namespace links and
search/permitted paths from the parent namespace.

Bug: http://b/37854032
Test: bionic_unit_tests --gtest_filter=dl*:Dl*
Change-Id: I174661d4a1dd0cbe4a378179073719aa955f3592
(cherry picked from commit ec43dd6c36d75014c4e4dc592dd67ab20033a76a)
diff --git a/linker/linker_namespaces.h b/linker/linker_namespaces.h
index e7d9b2e..c3260fd 100644
--- a/linker/linker_namespaces.h
+++ b/linker/linker_namespaces.h
@@ -48,6 +48,10 @@
     return linked_namespace_;
   }
 
+  const std::unordered_set<std::string>& shared_lib_sonames() const {
+    return shared_lib_sonames_;
+  }
+
   bool is_accessible(const char* soname) const {
     return shared_lib_sonames_.find(soname) != shared_lib_sonames_.end();
   }