OOP PDF: Change the save toolbar button to match the save menu behavior.

OOP PDF: Change the save toolbar button to match the save menu behavior.

Previously, the save toolbar button for the out-of-process PDF plugin
was a link to the PDF URL. This did not function for file URLs or PDFs
returned in response to a POST. This changes the button to use the
pepper PDF save API and adds a way for a WebContentsDelegate to override
SaveFrame behavior so the MimeHandlerViewGuest can instruct its embedder
to handle the actual save.

BUG=416329
TEST=Run with --out-of-process-pdf.
Open a local PDF and click the save toolbar button. The save as dialog
should appear.
Repeat the same with a PDF returned by a POST request. Saving should
save the opened PDF - not the page returned by a GET to the same URL.

Committed: https://crrev.com/92af61555dff60e1d1b51c47d27d07c5a643726d
Cr-Commit-Position: refs/heads/master@{#304920}

[Sam McNally, 2014-11-13 00:48:53]

sammc@chromium.org changed reviewers:
+ raymes@chromium.org

[Sam McNally, 2014-11-13 04:31:15]

Patchset #1 (id:1) has been deleted

[raymes, 2014-11-13 06:30:06]

lgtm

[raymes, 2014-11-13 06:31:07]

raymes@chromium.org changed reviewers:
+ fsamuel@chromium.org

[raymes, 2014-11-13 06:31:08]

+fsamuel@ for browser-plugin related code

[Fady Samuel, 2014-11-13 14:53:28]

guest_view lgtm

[Sam McNally, 2014-11-13 22:40:20]

sammc@chromium.org changed reviewers:
+ jam@chromium.org

[Sam McNally, 2014-11-13 22:40:21]

+jam for content

[jam, 2014-11-14 17:32:29]

lgtm

[Sam McNally, 2014-11-16 23:29:21]

sammc@chromium.org changed reviewers:
+ kenrb@chromium.org

[Sam McNally, 2014-11-16 23:29:22]

+kenrb for extensions/common/extension_messages.h

[Sam McNally, 2014-11-19 03:55:20]

kenrb: ping

[kenrb, 2014-11-19 16:45:02]

Sorry for the delay.

ipc lgtm

[Sam McNally, 2014-11-19 22:31:22]

The CQ bit was checked by sammc@chromium.org

[commit-bot: I haz the power, 2014-11-19 22:32:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/706823004/40001

[commit-bot: I haz the power, 2014-11-19 23:27:54]

Committed patchset #2 (id:40001)

[commit-bot: I haz the power, 2014-11-19 23:28:33]

Patchset 2 (id:??) landed as
https://crrev.com/92af61555dff60e1d1b51c47d27d07c5a643726d
Cr-Commit-Position: refs/heads/master@{#304920}