Define file contexts for WebViewBootstrap apex.

Set up minimal file_contexts for the com.android.webview.bootstrap APEX.

Bug: 318717084
Test: m com.android.webview.bootstrap
Change-Id: Id707617447dc44111891446eea442b31b7ff1b57
diff --git a/apex/com.android.webview.bootstrap-file_contexts b/apex/com.android.webview.bootstrap-file_contexts
new file mode 100644
index 0000000..9398505
--- /dev/null
+++ b/apex/com.android.webview.bootstrap-file_contexts
@@ -0,0 +1 @@
+(/.*)?           u:object_r:system_file:s0