Implement OnLegacySessionError() in CdmAdapter.

This is the same as OnSessionError() in CDM_6 implementation. It's needed to
properly support prefixed EME API.

Also roll src/media/cdm/ppapi/api 09203a7:4aca594 (svn 293431:293568)
Summary of changes available at:
https://chromium.googlesource.com/chromium/cdm/+log/09203a7..4aca594

BUG=428384

Review URL: https://codereview.chromium.org/820133003

Cr-Commit-Position: refs/heads/master@{#310636}
3 files changed