Merge to XFA: Tighten up DEPS include rules.

Original Review URL: https://codereview.chromium.org/1233583004 .
TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1234923006 .
diff --git a/testing/DEPS b/testing/DEPS
new file mode 100644
index 0000000..c7267d3
--- /dev/null
+++ b/testing/DEPS
@@ -0,0 +1,4 @@
+include_rules = [
+  '+core/include',
+  '+fpdfsdk/include',
+]
\ No newline at end of file