Merge "Use a concurrent hash map to access VolumeDialogControllerImpl's callbacks" am: ce7d32096e am: 333fdf8c59 am: 19797c2dd6

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1247026

Change-Id: I727723ed6f0685b43b499453256ae3de8c7d65e5