/analyze on Windows complains about using HRESULT in a Boolean context,
so check returned values using the appropriate macro.

BUG=687394
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2669083002
Cr-Commit-Position: refs/heads/master@{#447925}