[9] RFR (S): 8068183: Add isTieredSupported method to c.o.j.t.Platforms

[Filipp Zhinkin]

Hi all,

please review a new c.o.j.t.Platform's method "isTieredSupported"
which is aimed to report whether or not JVM supports tiered compilation
disregard to TieredCompilation flag's value.

Such functionality is required for Segmented Code Cache CLI tests [1]
and it would be useful in other cases too ([2] for instance).

In order to check if tiered compilation is supported we simply look to
"sun.management.compiler"property's valuewhich will contain
"Tiered Compilers" substring only when tiered compilation is supported [3].

Bug id: https://bugs.openjdk.java.net/browse/JDK-8068183
Webrev: http://cr.openjdk.java.net/~fzhinkin/8068183/webrev.00/
Testing: manual on localmachine using both client & server JVMs.

Thanks,
Filipp.

[1] 
http://mail.openjdk.java.net/pipermail/hotspot-compiler-dev/2014-December/016717.html
[2] https://bugs.openjdk.java.net/browse/JDK-8067823
[3] 
http://hg.openjdk.java.net/jdk9/jdk9/hotspot/file/7f062b70a344/src/share/vm/prims/jvm.cpp#l366