Rename MediaClientAndroid to MediaDrmBridgeClient

MediaClient and MediaClientAndroid (now MediaDrmBridgeClient)
are distict interfaces. The previous naming wrongly suggests that
MediaClientAndroid is the Android implementation of MediaClient.

BUG=695264

Review-Url: https://codereview.chromium.org/2756333002
Cr-Commit-Position: refs/heads/master@{#458783}
27 files changed