Merge "Simplify synchronized code and add comments" am: 9791b54b88 am: b57f32e68a am: 9760c42784 am: ddf2351c06

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

Change-Id: I2e618decc9e501f76c86b1382dc0a1341ed50fac