Fix plugin grouping for PDF in about:plugins

chrome/browser/resources/plugin_metadata/plugins_linux.json

 {
   "x-version": 5,
   "google-talk": {
     "mime_types": [
     ],
     "versions": [
       {
         "version": "0",
         "status": "requires_authorization",
         "comment": "'Google Talk Plugin' and 'Google Talk Plugin Video Accelerator' use two completely different versioning schemes, so we can't define a minimum version."
@@ skipping 105 matching lines @@
     ],
     "versions": [
       {
         "version": "0",
         "status": "up_to_date",
         "comment": "Google Chrome PDF has no version information."
       }
     ],
     "name": "Chrome PDF Viewer",
     "group_name_matcher": "*Chrome PDF Viewer*"
+  },
+  "chromium-pdf": {
+    "mime_types": [
+    ],
+    "versions": [
+      {
+        "version": "0",
+        "status": "up_to_date",
+        "comment": "Chrome PDF Viewer has no version information."
+      }
+    ],
+    "name": "Chromium PDF Viewer",
+    "group_name_matcher": "*Chromium PDF Viewer*"
   }
 }