Aligned srcset mixedContent blocking to the spec

Aligned srcset mixedContent blocking to the spec

Previous implementation did not block mixed content when the srcset attribute was empty.
This CL fixes that.

BUG=402792
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=180059

[Mike West, 2014-08-12 08:05:05]

On 2014/08/12 07:59:53, Yoav Weiss wrote:

LGTM if you add a test that checks this case rather than overwriting the test
that checks the other case. :)

[Yoav Weiss, 2014-08-12 08:14:33]

On 2014/08/12 08:05:05, Mike West wrote:
> On 2014/08/12 07:59:53, Yoav Weiss wrote:
> 
> LGTM if you add a test that checks this case rather than overwriting the test
> that checks the other case. :)

Fair enough :)

[Mike West, 2014-08-12 08:15:53]

SLGTM, thanks!

[Mike West, 2014-08-12 08:15:59]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-08-12 08:17:01]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/yoav@yoav.ws/467533002/20001

[commit-bot: I haz the power, 2014-08-12 09:24:34]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/22227)

[commit-bot: I haz the power, 2014-08-12 10:34:24]

Change committed as 180059