[Telemetry] Set youtube system health benchmarks to have platform specific recordings.

tools/perf/page_sets/data/system_health_desktop.json

 {
     "archives": {
         "browse:media:imgur": {
             "DEFAULT": "system_health_desktop_025.wpr"
         },
         "browse:media:pinterest": {
             "DEFAULT": "system_health_desktop_035.wpr"
         },
         "browse:media:tumblr": {
             "DEFAULT": "system_health_desktop_036.wpr"
         },
         "browse:media:youtube": {
-            "DEFAULT": "system_health_desktop_026.wpr"
+            "DEFAULT": "system_health_desktop_026.wpr",
+            "linux": "system_health_desktop_026.wpr"
         },
         "browse:news:cnn": {
             "DEFAULT": "system_health_desktop_013.wpr"
         },
         "browse:news:flipboard": {
             "DEFAULT": "system_health_desktop_021.wpr"
         },
         "browse:news:hackernews": {
             "DEFAULT": "system_health_desktop_014.wpr"
         },
@@ skipping 39 matching lines @@
         "load:media:google_images": {
             "DEFAULT": "system_health_desktop_003.wpr"
         },
         "load:media:imgur": {
             "DEFAULT": "system_health_desktop_025.wpr"
         },
         "load:media:soundcloud": {
             "DEFAULT": "system_health_desktop_003.wpr"
         },
         "load:media:youtube": {
-            "DEFAULT": "system_health_desktop_003.wpr"
+            "DEFAULT": "system_health_desktop_003.wpr",
+            "linux": "system_health_desktop_003.wpr"
         },
         "load:news:bbc": {
             "DEFAULT": "system_health_desktop_002.wpr"
         },
         "load:news:cnn": {
             "DEFAULT": "system_health_desktop_006.wpr"
         },
         "load:news:flipboard": {
             "DEFAULT": "system_health_desktop_020.wpr"
         },
@@ skipping 89 matching lines @@
         },
         "play:media:soundcloud": {
             "DEFAULT": "system_health_desktop_030.wpr"
         },
         "search:portal:google": {
             "DEFAULT": "system_health_desktop_022.wpr"
         }
     },
     "description": "Describes the Web Page Replay archives for a story set. Don't edit by hand! Use record_wpr for updating.",
     "platform_specific": true
-}
+}