RFR: 8215368: Make Check.checkOverride call diagnosticPositionFor lazily

[Maurizio Cimadamore]

Looks good

Thanks
Maurizio

On 13/12/2018 19:08, Liam Miller-Cushon wrote:
> Hi,
>
> Please consider this trivial performance fix to Check.checkOverride, 
> which achieved roughly a 2x speedup on a compilation of a pathological 
> generated source file.
>
> bug: https://bugs.openjdk.java.net/browse/JDK-8215368
> webrev: http://cr.openjdk.java.net/~cushon/8215368/webrev.00