ash: Fix clusterfuzz crash in AddShelfOptionsMenu

ash: Fix clusterfuzz crash in AddShelfOptionsMenu

Ash ShelfDelegate is created on session state change to ACTIVE
via mojo asynchronously. Mouse events could happen during that
time to trigger shelf context menu and crash. Replace DCHECK
with an "if" to handle such case since it is possible now.

BUG=690902
TEST=clusterfuzz

Review-Url: https://codereview.chromium.org/2693513002
Cr-Commit-Position: refs/heads/master@{#449743}
Committed: https://chromium.googlesource.com/chromium/src/+/70adf8ced0a1e191f0dabdec73b568c26f1ca2d2

[xiyuan, 2017-02-10 19:31:40]

The CQ bit was checked by xiyuan@chromium.org to run a CQ dry run

[xiyuan, 2017-02-10 19:32:09]

xiyuan@chromium.org changed reviewers:
+ jamescook@chromium.org

[commit-bot: I haz the power, 2017-02-10 19:33:10]

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

[James Cook, 2017-02-10 20:25:02]

LGTM

Aside: I've seen a few clusterfuzz crashes related to it generating mouse events
that happen very early during startup. It's unclear to me if these can happen in
production. I think there would have to be an input event after login but before
the shelf is created. Do you think that can happen? Is there something we could
do to guard against this problem in general?

[commit-bot: I haz the power, 2017-02-10 20:49:10]

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

[commit-bot: I haz the power, 2017-02-10 20:49:11]

Dry run: This issue passed the CQ dry run.

[xiyuan, 2017-02-10 21:32:18]

On 2017/02/10 20:25:02, James Cook wrote:
> LGTM
> 
> Aside: I've seen a few clusterfuzz crashes related to it generating mouse
events
> that happen very early during startup. It's unclear to me if these can happen
in
> production. I think there would have to be an input event after login but
before
> the shelf is created. Do you think that can happen? Is there something we
could
> do to guard against this problem in general?

In this particular crash, clusterfuzz runs chrome with --login-user so it skips
login and runs the crash-n-restart code path. PreMainMessageLoopRun ->
PostProfileInit -> StartRestoreAfterCrashSession sets session state to active.
After that, main thread is started. Since mojo is asynchronously so the shelf is
probably not yet created when the main thread starts. In theory, input events
could be handled before the mojo message that creates the shelf gets picked up.

Not sure what is the best way to prevent this in general. :(

[xiyuan, 2017-02-10 21:33:40]

The CQ bit was checked by xiyuan@chromium.org

[commit-bot: I haz the power, 2017-02-10 21:34:26]

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

[commit-bot: I haz the power, 2017-02-10 21:40:33]

CQ is committing da patch.

Bot data: {"patchset_id": 1, "attempt_start_ts": 1486762420397730, "parent_rev":
"6fbd4b4aee1e86ec3eac59fe600c9ebd53af1db9", "commit_rev":
"70adf8ced0a1e191f0dabdec73b568c26f1ca2d2"}

[commit-bot: I haz the power, 2017-02-10 21:41:17]

Description was changed from

==========
ash: Fix clusterfuzz crash in AddShelfOptionsMenu

Ash ShelfDelegate is created on session state change to ACTIVE
via mojo asynchronously. Mouse events could happen during that
time to trigger shelf context menu and crash. Replace DCHECK
with an "if" to handle such case since it is possible now.

BUG=690902
TEST=clusterfuzz
==========

to

==========
ash: Fix clusterfuzz crash in AddShelfOptionsMenu

Ash ShelfDelegate is created on session state change to ACTIVE
via mojo asynchronously. Mouse events could happen during that
time to trigger shelf context menu and crash. Replace DCHECK
with an "if" to handle such case since it is possible now.

BUG=690902
TEST=clusterfuzz

Review-Url: https://codereview.chromium.org/2693513002
Cr-Commit-Position: refs/heads/master@{#449743}
Committed:
https://chromium.googlesource.com/chromium/src/+/70adf8ced0a1e191f0dabdec73b5...
==========

[commit-bot: I haz the power, 2017-02-10 21:41:18]

Committed patchset #1 (id:1) as
https://chromium.googlesource.com/chromium/src/+/70adf8ced0a1e191f0dabdec73b5...