Fix NULL pointer dereference in FinishedAsyncCopyRequest()

Fix NULL pointer dereference in FinishedAsyncCopyRequest()

Due to undefined (favorably right to left) argument evaluation order,
the tracker might have been passed and set to NULL before the window
is looked up which results in a NULL pointer dereference.

BUG=659210
Review-Url: https://chromiumcodereview.appspot.com/2435033002
Cr-Commit-Position: refs/heads/master@{#426748}
(cherry picked from commit 1b4c64279b7c212242738b96643a0700d04d725c)

Committed: https://chromium.googlesource.com/chromium/src/+/149b81a0e8d4ef9ea107489aa62b6ffc429cba21

[Sergey Ulanov, 2016-10-31 18:40:19]

Description was changed from

==========
Fix NULL pointer dereference in FinishedAsyncCopyRequest()

Due to undefined (favorably right to left) argument evaluation order,
the tracker might have been passed and set to NULL before the window
is looked up which results in a NULL pointer dereference.

BUG=659210

Review-Url: https://chromiumcodereview.appspot.com/2435033002
Cr-Commit-Position: refs/heads/master@{#426748}
(cherry picked from commit 1b4c64279b7c212242738b96643a0700d04d725c)
==========

to

==========
Fix NULL pointer dereference in FinishedAsyncCopyRequest()

Due to undefined (favorably right to left) argument evaluation order,
the tracker might have been passed and set to NULL before the window
is looked up which results in a NULL pointer dereference.

BUG=659210

Review-Url: https://chromiumcodereview.appspot.com/2435033002
Cr-Commit-Position: refs/heads/master@{#426748}
(cherry picked from commit 1b4c64279b7c212242738b96643a0700d04d725c)

Committed:
https://chromium.googlesource.com/chromium/src/+/149b81a0e8d4ef9ea107489aa62b...
==========

[Sergey Ulanov, 2016-10-31 18:40:20]

Committed patchset #1 (id:1) manually as
149b81a0e8d4ef9ea107489aa62b6ffc429cba21.