RFR 8209087: Clean up runtime code that compares 'this' to NULL

[Harold David Seigel]

Hi,

Please review this JDK-12 fix for JDK-8209087.  This fix removes 
comparisons of 'this' to 'NULL' from the three remaining methods 
containing this code.  Callers of these methods were looked at to see if 
their calling object might be NULL.  If so, then checks for NULL were 
added to these callers.

Open Webrev: 
http://cr.openjdk.java.net/~hseigel/bug_8209087/webrev/index.html

JBS Bug:  https://bugs.openjdk.java.net/browse/JDK-8209087

The fix was tested by running Mach5 tiers 1 and 2 tests and builds on 
Linux-x64, Windows, and Mac OS X, running tiers 3-5 tests on Linux-x64, 
and by running JCK-12 Lang and VM tests on Linux-x64.

Thanks, Harold