Merge "Simplify synchronized code and add comments" am: 9791b54b88 am: b57f32e68a am: 9760c42784

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1416212

Change-Id: Ic8a04251bb1d6b35b0516525fc8ac6eea06c537e