Media2: Fix crash in MediaBrowserLegacyTest
Media2: Fix crash in MediaBrowserLegacyTest

MediaBrowserLegacyTest create MediaSessionCompat directly, so we need
MediaButtonReceiver for the MediaSessionCompat.

Bug: 128264488
Test: $ ./gradlew media2:connectedCheck (on emulator with API 19)
Change-Id: I7b8cd7bad7329e94eb79e572a4938e89654f65f9

androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx