Ensures that there is no race condition in memory backed expectation store.
Ensures that there is no race condition in memory backed expectation store.

BUG=skia:

Review URL: https://codereview.chromium.org/659803002

Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot