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: I5cb99d76f8f7e38a6f3a03b18ec948c00bf34799