Add perf tests for starting Chrome with URL

tools/perf/page_sets/startup_pages.json

+{
+  "description": "Pages for testing starting Chrome with a URL",
+  "description": "Use record_wpr startup_pages_record to record data for this test",

[jeremy, 2013/12/15 13:03:36]

Why 2 description keys?

[aberent, 2013/12/16 17:07:43]

A mistake :-(. However JSON doesn't allow multiline strings, so I have had to
make the description into a list of strings to make it readable. I don't think
the description is used anywhere in the code, so this should be okay.

+  "archive_data_file": "data/startup_pages.json",
+  "pages": [
+    {
+      "url": "about:blank",
+      "why": "typical page",
+      "navigate_steps" : [
+        {"action": "set_startup_url", "startup_url": "about:blank"},
+        {"action": "wait", "seconds": 10 }
+      ]
+    },
+    {
+      "url": "http://news.bbc.co.uk",
+      "why": "typical page",
+      "navigate_steps" : [
+        {"action": "set_startup_url", "startup_url": "http://news.bbc.co.uk"},
+        {"action": "wait", "seconds": 10 }
+      ]
+    },
+    {
+      "url": "http://kapook.com",
+      "why": "Horribly complex page - stress test!",
+      "navigate_steps" : [
+        {"action": "set_startup_url", "startup_url": "http://kapook.com"},
+        {"action": "wait", "seconds": 10 }
+      ]
+    }
+  ]
+}