Update pdfium.py to support running pdfium tests with Dr. Memory

scripts/slave/gatekeeper.json

 {
   "comment": ["This is a configuration file for gatekeeper_ng.py",
               "Look at that for documentation on this file's format."],
 
   "masters": {
     "https://build.chromium.org/p/chromium": [
       {
         "categories": [
           "chromium_tree_closer"
         ],
@@ skipping 477 matching lines @@
         "tree_notify": [
             "bradnelson@chromium.org"
         ]
       }
     ],
     "https://build.chromium.org/p/client.pdfium": [
       {
         "categories": [
           "pdfium_all"
         ],
+        "excluded_builders" : [
+          "drm_win_xfa"
+        ],
         "builders": {
           "*": {}
         },
         "tree_notify": [
             "thestig@chromium.org",
             "tsepez@chromium.org"
         ]
       }
     ],
     "https://build.chromium.org/p/client.v8": [
@@ skipping 361 matching lines @@
         "svnkill",
         "taskkill"
       ],
       "closing_optional": [
         "compile",
         "gn"
       ]
     }
   }
 }