Add Win32k lockdown for PPAPI processes to finch testing parameters.

testing/variations/fieldtrial_testing_config_win.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
@@ skipping 82 matching lines @@
     "EnableMediaRouterWithCastExtension": [
         {
             "group_name": "Enabled"
         }
     ],
     "EnableSessionCrashedBubbleUI": [
         {
             "group_name": "Enabled"
         }
     ],
+    "EnableWin32kLockDownMimeTypes": [
+        {
+            "group_name": "PPAPILockdown_Enabled",
+            "params": {
+                "*": "Enabled"
+            }
+        }
+    ],
     "ExpectCTReporting": [
         {
             "enable_features": [
                 "ExpectCTReporting"
             ],
             "group_name": "ExpectCTReportingEnabled"
         }
     ],
     "ExtensionActionRedesign": [
         {
@@ skipping 383 matching lines @@
     ],
     "use-new-media-cache": [
         {
             "enable_features": [
                 "use-new-media-cache"
             ],
             "group_name": "Enabled"
         }
     ]
 }