Make system properties read only.

The issue is that some parts of the system libraries
(and the runtime) assume that these properties are
immutable. This change enforces that notion and makes
behaviour a lot more predictable.

This is not a backwards compatible change, but based
on analysis of code available to me I couldn't find any
instances where this change would break any application.

Has the side effect of fixing..

bug: 12491204
bug: 12491159

Change-Id: I60c73713c97a4721d0b9781010333a9e9c883534
2 files changed