XFA: Update standalone.gypi and .gitignore to match master

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1394483005 .
diff --git a/.gitignore b/.gitignore
index 93df69f..3014ed6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 /build/gyp
 /buildtools
 /out
+/testing/corpus
 /testing/gmock
 /testing/gtest
 /v8