Use String8/16 c_str [tools]

Bug: 295394788
Test: make checkbuild
Change-Id: I82d6899d8c15a10b15399c39177290012bb5f13b
Merged-In: I82d6899d8c15a10b15399c39177290012bb5f13b
diff --git a/libs/androidfw/tests/TestHelpers.cpp b/libs/androidfw/tests/TestHelpers.cpp
index 10c0a4f..c6f657c 100644
--- a/libs/androidfw/tests/TestHelpers.cpp
+++ b/libs/androidfw/tests/TestHelpers.cpp
@@ -79,9 +79,9 @@
   }
 
   if (String8(expected_str) != *actual_str) {
-    return AssertionFailure() << actual_str->string();
+    return AssertionFailure() << actual_str->c_str();
   }
-  return AssertionSuccess() << actual_str->string();
+  return AssertionSuccess() << actual_str->c_str();
 }
 
 }  // namespace android