Revert corpus to last known working version.

Failures from last roll need diagnosis.
TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1023913002
diff --git a/DEPS b/DEPS
index 6d9460a..6df5c3a 100644
--- a/DEPS
+++ b/DEPS
@@ -5,7 +5,7 @@
     "https://chromium.googlesource.com/external/gyp",
 
   "testing/corpus":
-     "https://pdfium.googlesource.com/pdfium_tests@963fa2f89a051f611befcc1771dc0e66c859f493",
+     "https://pdfium.googlesource.com/pdfium_tests@1b25cea6e0472d89df747c9814ee4cb028c51247",
 
   "testing/gmock":
      "https://chromium.googlesource.com/external/googlemock.git@29763965ab52f24565299976b936d1265cb6a271",