Merge "Use a concurrent hash map to access VolumeDialogControllerImpl's callbacks" am: ce7d32096e am: 333fdf8c59 am: 19797c2dd6 am: 3f0535c610 am: e805a77383

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

Change-Id: I1b868fed6f3b46e95d737f349d8476aea5804041