[system health] Add desktop browsing story for facebook and change url of twitter story.

tools/perf/page_sets/data/system_health_desktop.json

 {
     "archives": {
         "system_health_desktop_000.wpr": [
             "load:search:amazon",
             "load:search:flipkart",
             "load:search:ebay",
             "load:search:google",
             "load:search:yandex",
             "load:search:taobao",
             "load:search:yahoo",
@@ skipping 44 matching lines @@
         ],
         "system_health_desktop_009.wpr": [
             "load:news:nytimes"
         ],
         "system_health_desktop_010.wpr": [
             "load:news:qq"
         ],
         "system_health_desktop_011.wpr": [
             "load:news:reddit"
         ],
-        "system_health_desktop_012.wpr": [
-            "load:social:twitter"
-        ],
         "system_health_desktop_013.wpr": [
             "browse:news:cnn"
         ],
         "system_health_desktop_014.wpr": [
             "browse:news:hackernews"
         ],
         "system_health_desktop_015.wpr": [
             "browse:news:nytimes"
         ],
         "system_health_desktop_016.wpr": [
             "browse:news:reddit"
         ],
-        "system_health_desktop_017.wpr": [
+        "system_health_desktop_018.wpr": [
+            "load:social:twitter"
+        ],
+        "system_health_desktop_019.wpr": [
             "browse:social:twitter"
         ]
     },
     "description": "Describes the Web Page Replay archives for a story set. Don't edit by hand! Use record_wpr for updating."
 }