Have two-way binding use localized variables to prevent NPE.

Bug 26962999

Two-way binding was using the inverted expressions directly
without localizing variables. That meant that if there was
a variable set to null during evaluation, it may get a
NullPointerException even though it checked for null
on the value previously. This CL localizes the variables
so that cannot happen.

Change-Id: Ia55955ce0f1cb750e6a678e72e0cda03f0e3c9b6
53 files changed