[system health] Add media browsing stories.

tools/perf/page_sets/data/system_health_desktop.json

Index: tools/perf/page_sets/data/system_health_desktop.json
diff --git a/tools/perf/page_sets/data/system_health_desktop.json b/tools/perf/page_sets/data/system_health_desktop.json
index f41de53199c1146160af96647b387a6ebee9e1e6..58e7d9e2b5ea110ed896e3fc6723e9d516b49639 100644
--- a/tools/perf/page_sets/data/system_health_desktop.json
+++ b/tools/perf/page_sets/data/system_health_desktop.json
@@ -85,7 +85,14 @@
         ],
         "system_health_desktop_021.wpr": [
             "browse:news:flipboard"
+        ],
+        "system_health_desktop_025.wpr": [
+            "browse:media:imgur",
+            "load:media:imgur"
+        ],
+        "system_health_desktop_026.wpr": [
+            "browse:media:youtube"
         ]
     },
     "description": "Describes the Web Page Replay archives for a story set. Don't edit by hand! Use record_wpr for updating."
-}
+}