Refactor PrivateScriptRunner.js to reduce the number of globally exposed variables

Refactor PrivateScriptRunner.js to reduce the number of globally exposed variables

It's not a good idea to use global variables in PrivateScriptRunner.js
because they are exposed to all window objects of the private scripts.
This CL reduces the number of global variables used in PrivateScriptRunner.js.

Also this CL removes a |global| parameter from installClass()
since the |global| is always equal to the window object of the JS file.

BUG=341031
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180053

[haraken, 2014-08-12 03:54:55]

jl@: PTAL. This is a simple refactoring.

[Jens Widell, 2014-08-12 04:41:15]

LGTM

[haraken, 2014-08-12 05:03:14]

The CQ bit was checked by haraken@chromium.org

[commit-bot: I haz the power, 2014-08-12 05:04:14]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/haraken@chromium.org/466623002/20001

[commit-bot: I haz the power, 2014-08-12 05:44:05]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/2...)
  linux_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/2...)
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/19390)
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/22188)

[commit-bot: I haz the power, 2014-08-12 05:52:44]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-08-12 05:52:45]

Try jobs failed on following builders:
  linux_blink_dbg on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_dbg/builds/2...)

[haraken, 2014-08-12 08:32:27]

The CQ bit was checked by haraken@chromium.org

[commit-bot: I haz the power, 2014-08-12 08:33:06]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/haraken@chromium.org/466623002/40001

[commit-bot: I haz the power, 2014-08-12 09:41:04]

Change committed as 180053