Web MIDI: stop sending messages when the document is going to be closed

Web MIDI: stop sending messages when the document is going to be closed

When the page is going to be closed, loader() may return nullptr.
In MIDIAccess::sendMIDIData(), we refer the DocumentLoader without any
check, thus it results in a renderer crash though it rarely happens.

I had a report on a similar issue, but the specific code in the case was
already removed. This patch also fixes another potential problem that
may cause the same issue.

BUG=674005
Committed: https://crrev.com/be3f5b8ec3199a8c6fbba72cbc83776d6ae53efc
Cr-Commit-Position: refs/heads/master@{#438485}

[Takashi Toyoshima, 2016-12-14 09:36:36]

Description was changed from

==========
Web MIDI: stop sending messages when the document is going to be closed

When the page is going to be closed, loader() may return nullptr.
In MIDIAccess::sendMIDIData(), we refer the DocumentLoader without any
check, thus it results in a renderer crash though it rarely happens.

I had a report on a similar issue, but the specific code in the case was
already removed. This patch also fixes another potential problem that
may cause the same issue.

BUG=674005
==========

to

==========
Web MIDI: stop sending messages when the document is going to be closed

When the page is going to be closed, loader() may return nullptr.
In MIDIAccess::sendMIDIData(), we refer the DocumentLoader without any
check, thus it results in a renderer crash though it rarely happens.

I had a report on a similar issue, but the specific code in the case was
already removed. This patch also fixes another potential problem that
may cause the same issue.

BUG=674005
==========

[Takashi Toyoshima, 2016-12-14 09:36:36]

toyoshim@chromium.org changed reviewers:
+ kouhei@chromium.org

[Takashi Toyoshima, 2016-12-14 09:38:59]

PTAL.
Probably we have similar potential problems here and there, especially around
Performance and Event creation?

[kouhei (in TOK), 2016-12-14 10:39:30]

The CQ bit was checked by kouhei@chromium.org

[kouhei (in TOK), 2016-12-14 10:39:30]

lgtm

lgtm as a short term fix, but I think webmidi shouldn't access DocumentLoader in
the first place.

[commit-bot: I haz the power, 2016-12-14 10:39:44]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Takashi Toyoshima, 2016-12-14 11:48:53]

So what's the good manner to obtain the document creation timestamp?

timing/Performance.cpp also accesses frame->document->loader() to generate
DOMHighResTimeStamp.
events/Event.cpp uses Performance to generate timeStamp. So, I guess
DocumentLoader is the only instance to know the creation timestamp.

Shall I access it indirectly via Performance instance?
Also probably I would make a copy of the timestamp as a MIDIAccess member in the
constructor.

[commit-bot: I haz the power, 2016-12-14 12:08:33]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1481711970542830, "parent_rev":
"080a8dad8b93db99ba8726200e41c529c3433ecb", "commit_rev":
"c896d6bbdbf260819ff087b749befbfc8fde344b"}

[commit-bot: I haz the power, 2016-12-14 12:09:01]

Description was changed from

==========
Web MIDI: stop sending messages when the document is going to be closed

When the page is going to be closed, loader() may return nullptr.
In MIDIAccess::sendMIDIData(), we refer the DocumentLoader without any
check, thus it results in a renderer crash though it rarely happens.

I had a report on a similar issue, but the specific code in the case was
already removed. This patch also fixes another potential problem that
may cause the same issue.

BUG=674005
==========

to

==========
Web MIDI: stop sending messages when the document is going to be closed

When the page is going to be closed, loader() may return nullptr.
In MIDIAccess::sendMIDIData(), we refer the DocumentLoader without any
check, thus it results in a renderer crash though it rarely happens.

I had a report on a similar issue, but the specific code in the case was
already removed. This patch also fixes another potential problem that
may cause the same issue.

BUG=674005

Review-Url: https://codereview.chromium.org/2566223006
==========

[commit-bot: I haz the power, 2016-12-14 12:09:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-12-14 12:11:22]

Description was changed from

==========
Web MIDI: stop sending messages when the document is going to be closed

When the page is going to be closed, loader() may return nullptr.
In MIDIAccess::sendMIDIData(), we refer the DocumentLoader without any
check, thus it results in a renderer crash though it rarely happens.

I had a report on a similar issue, but the specific code in the case was
already removed. This patch also fixes another potential problem that
may cause the same issue.

BUG=674005

Review-Url: https://codereview.chromium.org/2566223006
==========

to

==========
Web MIDI: stop sending messages when the document is going to be closed

When the page is going to be closed, loader() may return nullptr.
In MIDIAccess::sendMIDIData(), we refer the DocumentLoader without any
check, thus it results in a renderer crash though it rarely happens.

I had a report on a similar issue, but the specific code in the case was
already removed. This patch also fixes another potential problem that
may cause the same issue.

BUG=674005

Committed: https://crrev.com/be3f5b8ec3199a8c6fbba72cbc83776d6ae53efc
Cr-Commit-Position: refs/heads/master@{#438485}
==========

[commit-bot: I haz the power, 2016-12-14 12:11:23]

Patchset 1 (id:??) landed as
https://crrev.com/be3f5b8ec3199a8c6fbba72cbc83776d6ae53efc
Cr-Commit-Position: refs/heads/master@{#438485}