PointerMap test fails with AssertionError: expected {} to have own property 'set'

[jacobrossi]

Running grunt intern:pointerevents, you'll get:

TOTAL: tested 1 platforms, 1/32 tests failed (1 skipped)
Warning: Test main - PointerMap - PointerMap has Map API FAILED on chrome 43.0.2357.124 on Windows NT:
AssertionError: expected {} to have own property 'set'
  at Assertion.assertOwnProperty  <__intern\node_modules\chai\chai.js:1819:10>
  at <Assertion.ctx.(anonymous function) [as ownProperty] (http://localhost:9000/__intern/node_modules/chai/chai.js:3627:25)>
  at <tests\unit\pointermap.js:23:19>
  at Array.forEach  <native>
  at Test.<anonymous>  <tests\unit\pointermap.js:22:12>
  at Test.test  <tests\support\tdd.js:4:28>
  at Test.run  <__intern\lib\Test.js:169:19>
  at <__intern\lib\Suite.js:237:13>
  at signalListener  <__intern\node_modules\dojo\Deferred.js:37:21>
  at Promise.then.promise.then  <__intern\node_modules\dojo\Deferred.js:258:5> Use --force to continue.

Perhaps introduced by 8c6d453
@stuartpb can you take a look?