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

tools/perf/page_sets/top_25.json

Index: tools/perf/page_sets/top_25.json
diff --git a/tools/perf/page_sets/top_25.json b/tools/perf/page_sets/top_25.json
index f16c3b0cb462e73aaa9e9ce2e793c252119379f5..755aec7b2bd222c603e3bc37fa8d73243700cfbf 100644
--- a/tools/perf/page_sets/top_25.json
+++ b/tools/perf/page_sets/top_25.json
@@ -1,6 +1,6 @@
 {
     "description": "Pages hand-picked for 2012 CrOS scrolling tuning efforts.",
-    "archive_path": "../data/top_25.wpr",
+    "archive_data_file": "../data/top_25/index.json",

[dtu, 2013/01/23 21:07:02]

Are you updating all the page sets to use the new format?

[marja, 2013/01/24 16:03:33]

Yes, I'll need to add a similar kind of update to other pages sets in this CL,
because the old format won't work any more.

Also, I need to update the .wprs to have new file names. So I need these CLs:
1. src-internal, copy .wprs under new names, add metadata files
2. This CL
3. src-internal, remove old .wpr files

(Added the other .json file updates to this CL. I hadn't done that yet, since I
hadn't finalized the data directory layout. Now all the data will be in ../data,
and the json files will have the file names "dataset.json". All the data can
still be in the same directory...)

     "credentials_path": "../data/credentials.json",
     "user_agent_type": "desktop",
     "pages": [