Make DexFiles opened from files readonly by default, but writable during dex2oat

Bug: 9618388
Change-Id: I83f2e16ee8446a79a94a84971146d807bb0c9ee0
diff --git a/runtime/dex_file_test.cc b/runtime/dex_file_test.cc
index 6449493..32a8354 100644
--- a/runtime/dex_file_test.cc
+++ b/runtime/dex_file_test.cc
@@ -75,6 +75,8 @@
   ScopedObjectAccess soa(Thread::Current());
   const DexFile* dex_file = DexFile::Open(location, location);
   CHECK(dex_file != NULL);
+  EXPECT_EQ(PROT_READ, dex_file->GetPermissions());
+  EXPECT_TRUE(dex_file->IsReadOnly());
   return dex_file;
 }