CDM FileIOTest: Work around flakiness by not closing during read/write.

The flakiness is caused by issue 415401. Temporarily disable tests that close
the FileIO during pending read or write.

This also reenables ECKEncryptedMediaTest.FileIOTest by reverting commit
5af9a9c9d2d559014734c2eb2247d42f3fc0e740.

BUG=415401,415742

Review URL: https://codereview.chromium.org/582233003

Cr-Commit-Position: refs/heads/master@{#295726}
2 files changed