Two fixes for mojo JS bindings

Two fixes for mojo JS bindings

Makes WaitingCallback cancel a wait if there is a wait pending and
it's deleted.
Makes MessagePumpMojo deal with MOJO_RESULT_CANCELLED.

BUG=371755
TEST=see bug
R=darin@chromium.org, mpcomplete@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269663

[sky, 2014-05-09 21:57:30]

darin: MessagePumpMojo
mpcomplete: the rest

[darin (slow to review), 2014-05-09 22:00:15]

LGTM

https://codereview.chromium.org/276093002/diff/20001/mojo/common/message_pump...
File mojo/common/message_pump_mojo.cc (right):

https://codereview.chromium.org/276093002/diff/20001/mojo/common/message_pump...
mojo/common/message_pump_mojo.cc:165: NOTREACHED();
should this CHECK(false) so we learn if this ever happens in the field? you
might also use base::debug::Alias to ensure that |result| is available in crash
reports.

[sky, 2014-05-09 22:04:51]

https://codereview.chromium.org/276093002/diff/20001/mojo/common/message_pump...
File mojo/common/message_pump_mojo.cc (right):

https://codereview.chromium.org/276093002/diff/20001/mojo/common/message_pump...
mojo/common/message_pump_mojo.cc:165: NOTREACHED();
On 2014/05/09 22:00:15, darin wrote:
> should this CHECK(false) so we learn if this ever happens in the field? you
> might also use base::debug::Alias to ensure that |result| is available in
crash
> reports.

Done.

[Matt Perry, 2014-05-09 22:16:44]

lgtm

[sky, 2014-05-09 22:20:20]

The CQ bit was checked by sky@chromium.org

[commit-bot: I haz the power, 2014-05-09 22:25:13]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/sky@chromium.org/276093002/60001

[commit-bot: I haz the power, 2014-05-10 02:10:20]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-05-11 00:56:24]

Change committed as 269663