Remove 'WebURLRequest::TargetType' from PrefetchHelper.

Remove 'WebURLRequest::TargetType' from PrefetchHelper.

'WebURLRequest::TargetType' has been dropped in Blink in favor of
'RequestContext' and 'FrameType', matching the Fetch specification's
changes, and allowing both more granularity in various Blink-side checks
and more clarity around the thing that caused a request, and the frame
that the request affects.

This CL should have zero practical effect, as it's simply hoisting the
translation work that 'WebURLRequest::setTargetType' is already doing
up into the content layer to bring us one step closer to removing the
concept entirely.

BUG=390497
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284565

[Mike West, 2014-07-21 16:17:43]

thestig@: Mind taking a look at this CL?

jochen@: FYI, since you're on all the other CLs in the series.

-mike

[Lei Zhang, 2014-07-21 18:57:47]

lgtm

[commit-bot: I haz the power, 2014-07-21 18:59:53]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/407883005/1

[commit-bot: I haz the power, 2014-07-21 20:50:20]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)
  win_chromium_x64_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_x64_rel/...)

[commit-bot: I haz the power, 2014-07-21 21:31:53]

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

[commit-bot: I haz the power, 2014-07-21 21:31:54]

Try jobs failed on following builders:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[Lei Zhang, 2014-07-21 21:32:39]

The CQ bit was checked by thestig@chromium.org

[commit-bot: I haz the power, 2014-07-21 21:35:01]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/407883005/1

[commit-bot: I haz the power, 2014-07-22 00:46:44]

Change committed as 284565