Telemetry: add a metadata layer between page set and .wpr.

tools/perf/page_sets/top_25.json

 {
     "description": "Pages hand-picked for 2012 CrOS scrolling tuning efforts.",
-    "archive_path": "../data/top_25.wpr",
+    "archive_data_file": "../data/top_25.json",
     "credentials_path": "../data/credentials.json",
     "user_agent_type": "desktop",
     "pages": [
         {
             "url": "https://www.google.com/#hl=en&q=barack+obama",
             "why": "top google property; a google tab is often open",
             "smoothness": {
                 "action": "scrolling_action"
             },
             "wait_for_element_with_text": "Next",
@@ skipping 479 matching lines @@
         },
         {
             "url": "http://techcrunch.com",
             "why": "top tech blog",
             "smoothness": {
                 "action": "scrolling_action"
             }
         }
     ]
 }