PPAPI: Disallow blocking callbacks while handling a blocking message

PPAPI: Disallow blocking callbacks while handling a blocking message

This makes it so that the plugin can not use blocking completion callbacks while servicing HandleBlockingMessage. This is to discourage leaving JavaScript hung while doing long-running things (e.g. file IO).

(Of course, the plugin can get around this by bouncing to another thread; but I think this adds a useful guideline/deterrent.)

BUG=415351
Committed: https://crrev.com/44b96754c1e11929fd7d1dc8ed36880d80476372
Cr-Commit-Position: refs/heads/master@{#296422}

[dmichael (off chromium), 2014-09-23 20:17:16]

dmichael@chromium.org changed reviewers:
+ teravest@chromium.org

[teravest, 2014-09-23 20:23:01]

Some more reasoning in the commit description would be nice. The logic here
looks fine, I think.

https://codereview.chromium.org/600553002/diff/1/ppapi/api/pp_errors.idl
File ppapi/api/pp_errors.idl (right):

https://codereview.chromium.org/600553002/diff/1/ppapi/api/pp_errors.idl#newc...
ppapi/api/pp_errors.idl:144: * Returned if you try to use a null completion
callback to "block until
nit: This doesn't seem consistent with the style of other comments.
nit: "servicing a blocking Javascript is not..." sounds weird.

I'd suggest something more like:
Indicates that a null completion callback was used on a thread handling a
blocking message from JavaScript. Null completion callbacks "block until
complete", but blocking while servicing a blocking Javascript message is not
permitted... and so on.

[dmichael (off chromium), 2014-09-23 21:48:35]

comments addressed, PTAL

[teravest, 2014-09-23 23:13:31]

lgtm

[dmichael (off chromium), 2014-09-23 23:20:18]

The CQ bit was checked by dmichael@chromium.org

[commit-bot: I haz the power, 2014-09-23 23:22:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/600553002/20001

[commit-bot: I haz the power, 2014-09-24 00:01:39]

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

[commit-bot: I haz the power, 2014-09-24 00:01:40]

Try jobs failed on following builders:
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)

[dmichael (off chromium), 2014-09-24 15:28:00]

The CQ bit was checked by dmichael@chromium.org

[commit-bot: I haz the power, 2014-09-24 15:28:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/600553002/20001

[commit-bot: I haz the power, 2014-09-24 15:41:21]

Committed patchset #2 (id:20001) as 6ec110bb944a6484ea69b8a5ea8099cbd1eb7002

[commit-bot: I haz the power, 2014-09-24 15:42:11]

Patchset 2 (id:??) landed as
https://crrev.com/44b96754c1e11929fd7d1dc8ed36880d80476372
Cr-Commit-Position: refs/heads/master@{#296422}