Merge "MediaRouter2: Add missing synchronized(sRouterLock) block" into rvc-dev am: 5aacc569c7

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/11782206

Change-Id: Ic6c6de8245bd6b4e5365df4d591b87cfd3ef5461