Make graph tool of dmprof useful

Make a graph tool of dmprof useful.

1. Change the graph from bar-chart to area chat.
Now x-axis shows time line.  It is instinctive.

2. Enable to choose policies in GUI.
It is a waste of time to apply many policies and make different HTML files.
Now it can be done with clicks.  No need to specify a policy in converting json to HTML.

Usage:
$ dmprof /path/to/first.heap > temp.json
$ graph.py temp.json > graph.html  # no need to specify a poilcy
$ chrome graph.html    # open the HTML file in Chrome


BUG=None
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=255764

[peria, 2014-03-07 07:48:59]

Hi Mikurube-san,
Would you take a look?


I know graph.py is a mid-way tool, but it must be a best tool
to visualize the result of dmprof at this time.
I think this improvement makes some developers happy. :)

[kouhei (in TOK), 2014-03-07 07:58:34]

lgtm

[Dai Mikurube (NOT FULLTIME), 2014-03-07 20:41:29]

lgtm

[Dai Mikurube (NOT FULLTIME), 2014-03-07 20:41:30]

lgtm

lgtm

[peria, 2014-03-08 02:16:44]

The CQ bit was checked by peria@chromium.org

[commit-bot: I haz the power, 2014-03-08 11:18:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/peria@chromium.org/189623009/20001

[commit-bot: I haz the power, 2014-03-08 12:04:11]

Change committed as 255764