Check for null when getting the extension type.

Check for null when getting the extension type.

isJsInterop can call this with null.

BUG=
R=vsm@google.com

Committed: https://github.com/dart-lang/sdk/commit/4f7fa8a930cf7572ff42b85e5b00325e35326499

[Leaf, 2017-07-13 23:45:56]

leafp@google.com changed reviewers:
+ vsm@google.com

[vsm, 2017-07-13 23:47:16]

lgtm

[Leaf, 2017-07-13 23:48:36]

Description was changed from

==========
Check for null when getting the extension type.

isJsInterop can call this with null.

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

to

==========
Check for null when getting the extension type.

isJsInterop can call this with null.

BUG=
R=vsm@google.com

Committed:
https://github.com/dart-lang/sdk/commit/4f7fa8a930cf7572ff42b85e5b00325e35326499
==========

[Leaf, 2017-07-13 23:48:38]

Committed patchset #1 (id:1) manually as
4f7fa8a930cf7572ff42b85e5b00325e35326499 (presubmit successful).

[Jennifer Messerly, 2017-07-14 08:13:25]

jmesserly@google.com changed reviewers:
+ jmesserly@google.com

[Jennifer Messerly, 2017-07-14 08:13:26]

hmm, it might be better to figure out who's calling this with null, otherwise
this will slow down several potentially hot code paths

[Leaf, 2017-07-14 20:14:35]

On 2017/07/14 08:13:26, Jennifer Messerly wrote:
> hmm, it might be better to figure out who's calling this with null, otherwise
> this will slow down several potentially hot code paths

Yeah, that was the other fix I considered, but I worried about robustness.  If
we want to make this an invariant that it's never called with null I should be
able to track down all uses.  I'm not really convinced the null check is going
to matter relative to the cost of the helper call and the lookup of a missing
symbol, but doesn't hurt to keep it clean.  I'll take a look at it.