Set PPAPI plugins' requests' contexts to 'WebURLRequest::RequestContextPlugin'.

Set PPAPI plugins' requests' contexts to 'WebURLRequest::RequestContextPlugin'.

Pepper plugins' requests are piped through Blink's Fetch implementation,
giving us the opportunity to make policy decisions about whether or not
they should be allowed by CSP or Mixed Content (we're currently not
using this ability).

In order to make these decisions, we need to know that the request is
for data a plugin is requesting, as opposed to a plugin itself. This
patch adds that detail to PPAPI's URL-requesting logic.

BUG=390497
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284445

[Mike West, 2014-07-21 08:28:42]

Mind taking a look at this, Jochen?

-mike

[jochen (gone - plz use gerrit), 2014-07-21 11:29:32]

lgtm

[Mike West, 2014-07-21 11:45:33]

The CQ bit was checked by mkwst@chromium.org

[commit-bot: I haz the power, 2014-07-21 11:46:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/409563002/1

[commit-bot: I haz the power, 2014-07-21 15:04:28]

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

[commit-bot: I haz the power, 2014-07-21 16:46:42]

Change committed as 284445