Remove GetBlockingPool() usage in PrinterCapabilitiesTest.

The function being tested only cares about enforcing ThreadRestrictions
now. Since the unit test does not enforce ThreadRestrictions, just call
the function being tested.

Also put the test in the printing namespace.

BUG=667892

Review-Url: https://codereview.chromium.org/2959823003
Cr-Commit-Position: refs/heads/master@{#482714}
1 file changed