Bug fix in browser testing: add null check.

Fix an error where html_test (which is usually null) is used without checking for null, when reporting status back to the test controller.

BUG=
R=ahe@google.com

Committed: https://github.com/dart-lang/sdk/commit/ac23816bb721ffc40b2e0f1af7400b65233a7f8a

[Bill Hesse, 2017-04-06 14:36:10]

Patchset #1 (id:1) has been deleted

[Bill Hesse, 2017-04-06 14:36:29]

whesse@google.com changed reviewers:
+ ahe@google.com

[Bill Hesse, 2017-04-06 14:54:02]

Description was changed from

==========
Remove error from test scripts' browser driver window script.

BUG=
==========

to

==========
Fix an error where html_test (which is usually null) is used without checking
for null, when reporting status back to the test controller.

BUG=
==========

[ahe, 2017-04-06 14:56:00]

lgtm

[Bill Hesse, 2017-04-06 15:16:47]

Description was changed from

==========
Fix an error where html_test (which is usually null) is used without checking
for null, when reporting status back to the test controller.

BUG=
==========

to

==========
Fix an error where html_test (which is usually null) is used without checking
for null, when reporting status back to the test controller.

BUG=
R=ahe@google.com

Committed:
https://github.com/dart-lang/sdk/commit/ac23816bb721ffc40b2e0f1af7400b65233a7f8a
==========

[Bill Hesse, 2017-04-06 15:16:48]

Committed patchset #1 (id:20001) manually as
ac23816bb721ffc40b2e0f1af7400b65233a7f8a (presubmit successful).