Add "lax mixed content checking" runtime flag.

Add "lax mixed content checking" runtime flag.

For the same reasons that we're delaying the complete removal of
ShowModalDialog, we need to slow-walk the progress of tightening our
mixed content checks. This runtime-enabled setting will allow us to
set up a policy hook in order to provide enterprises with time to
adapt to the new-to-Chrome behavior of blocking mixed WebSockets and
XMLHttpRequest.

BUG=389089
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177110

[Mike West, 2014-06-27 11:04:29]

Hey Jochen, mind taking a look at this CL?

-mike

+saswat, FYI.

[jochen (gone - plz use gerrit), 2014-06-27 11:08:27]

lgtm

[Mike West, 2014-06-27 11:12:28]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-06-27 11:13:09]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/356843006/1

[commit-bot: I haz the power, 2014-06-27 12:08:18]

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/1...)
  linux_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/1...)
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/13101)
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/14066)

[Mike West, 2014-06-27 12:13:12]

The CQ bit was unchecked by mkwst@chromium.org

[Mike West, 2014-06-27 13:44:33]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-06-27 13:45:48]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/356843006/40001

[commit-bot: I haz the power, 2014-06-27 14:58:44]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  linux_gpu_triggered_tests on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/linux_gpu_trigger...)

[commit-bot: I haz the power, 2014-06-27 15:39:24]

Change committed as 177110