Add a "lifetime of bots" page; see sub group of bots for a subfleet (e.g. all XP, all GPU, etc)

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Use case:
- User specifies a filter flag, let's say state "gpu:1"
- Page fetches all bots with this state.
- For each bot:
  - Fetches recent events for last N hours. May require cursor iteration.
- Present events graph to show a visual representation of what happened in this 
bot groups.

The rationale is to be able to correlate when a group of bots misbehave.

The first thing is to add it for a single bot, then expand it to show multiple 
bots at once.

Action Items:
- Add API to search for bots per state value.
- Add API to retrieve events and tasks mixed together for N last hours.
- Add new page to show the UI.

Visualization ideas taken from https://github.com/marmelab/EventDrops:
https://github.com/marmelab/EventDrops
http://bl.ocks.org/rkirsling/33a9e350516da54a5d4f

In practice, I want something similar to:
http://build.chromium.org/p/chromium.swarm/waterfall?show_events=true&reload=120
&builder=Windows%20Swarm%20Tests&builder=Windows%20Swarm%20Tests%20(dbg)
where reboots and tasks are shown together.

Original issue reported on code.google.com by maruel@chromium.org on 27 Jan 2015 at 3:36

[GoogleCodeExporter]

Original comment by maruel@chromium.org on 18 Feb 2015 at 1:43

• Changed title: Add a "lifetime of bots" page; see sub group of bots for a subfleet (e.g. all XP, all GPU, etc)