Teach WebURLRequest about Fetch's "frame type" concept.

Teach WebURLRequest about Fetch's "frame type" concept.

This CL introduces a new enum property on resource requests which maps
to the "frame type" concept in Fetch[1]. The eventual goal is to migrate
mixed content and CSP checks which rely on knowledge of a request's
browsing context to use this new property rather than overloading the
request context with information about the request's browsing context
and originator.

To ensure that we can rely on the property's value, we ASSERT that the
value is properly set when loading "main" resources.

[1]: http://fetch.spec.whatwg.org/#concept-request-context-frame-type

BUG=390497
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178069

[Mike West, 2014-07-14 09:34:54]

Mind taking a look at this, Jochen? It should have zero web-visible effect, as
it's more groundwork for migrating CSP and MIX onto the new Fetch enums.

-mike

[jochen (gone - plz use gerrit), 2014-07-14 10:47:12]

lgtm

[Mike West, 2014-07-14 12:26:29]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-07-14 12:27:06]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/389993002/20001

[commit-bot: I haz the power, 2014-07-14 13:34:39]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/15297)

[commit-bot: I haz the power, 2014-07-14 14:29:05]

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

[commit-bot: I haz the power, 2014-07-14 14:29:06]

Try jobs failed on following builders:
  mac_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/mac_blink_rel/builds/15312)

[Mike West, 2014-07-14 14:53:46]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-07-14 14:54:52]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/389993002/20001

[commit-bot: I haz the power, 2014-07-14 15:38:05]

Change committed as 178069