Merge "Expand javadoc for Build.VERSION.KNOWN_CODENAMES." am: 4ff7b1d723 am: f8e89c239f am: 64d4a8e01a

Original change: https://android-review.googlesource.com/c/platform/frameworks/base/+/1979486

Change-Id: Ide5adfe60c9ce36948e22dea54b83667df55a8e7