Fix crash after Launcher drag/drop (take 3 - no unit test)

Fix crash after Launcher drag/drop (take 3 - no unit test)

BUG=439055
TEST=In Launcher, drag app to solitary folder on second page

Earlier versions of this CL included a unit test...
https://codereview.chromium.org/780023002/
https://codereview.chromium.org/792883006/
...but the slowness of valgrind kept screwing up the timing of the drag/drop,
so I'm giving up on the unit test (which didn't actually test this bug anyway).

Committed: https://crrev.com/e2a5c5df8bcc5571b451549cc8b6b4f99676b61b
Cr-Commit-Position: refs/heads/master@{#309575}

[Greg Levin, 2014-12-23 17:14:48]

glevin@chromium.org changed reviewers:
+ jennyz@chromium.org

[Greg Levin, 2014-12-23 17:14:48]

One more time, without the unit test.  Please have a quick look!

[jennyz, 2014-12-23 17:40:33]

The CQ bit was checked by jennyz@chromium.org

[commit-bot: I haz the power, 2014-12-23 17:41:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/823763003/1

[commit-bot: I haz the power, 2014-12-23 17:41:16]

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

[commit-bot: I haz the power, 2014-12-23 17:41:17]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[jennyz, 2014-12-23 18:51:28]

lgtm

[jennyz, 2014-12-23 18:51:32]

The CQ bit was checked by jennyz@chromium.org

[commit-bot: I haz the power, 2014-12-23 18:52:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/823763003/1

[commit-bot: I haz the power, 2014-12-23 19:45:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-23 19:46:50]

Patchset 1 (id:??) landed as
https://crrev.com/e2a5c5df8bcc5571b451549cc8b6b4f99676b61b
Cr-Commit-Position: refs/heads/master@{#309575}