Fix up HotwordServiceTest on Chrome-branded builds.
The ENABLE_HOTWORDING flag is not available in
hotword_service_unittest.cc, so all tests were assuming hotwording was
disabled (since r333548). This has been failing on Official builders
since r335874.
Since it's hard to resolve this in a simple way (we want to merge these
changes), just disabling the tests is the cleanest option for now.
BUG=503963
Review URL: https://codereview.chromium.org/
1207163002
Cr-Commit-Position: refs/heads/master@{#336091}