Merge "Use a concurrent hash map to access VolumeDialogControllerImpl's callbacks" am: ce7d32096e am: 333fdf8c59 am: 19797c2dd6 am: 3f0535c610

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

Change-Id: I032cdc7bf9972a3c990db8e3bef396ee14795690