Javadoc performance issue: Configuration.getText uses exceptional flow

[Claes Redestad]

Hi,

while profiling a few javadoc benchmarks that have regressed over the 
course of JDK 9, I noticed a couple of percent of the time is being 
spent throwing exceptions which are dealt with as a normal control flow.

This proof-of-concept patch exposes a way for the doclet code to ask the 
message provider if the key exists instead:

http://cr.openjdk.java.net/~redestad/scratch/javadoc_rb.01/

... and consistently show improvements from 3-19% over a range of 
javadoc microbenchmarks.

I've not been able to find a regression in our tracking that matches the 
improvement pattern, so this might have been around for a while. So if 
this patch looks reasonable I'll file the bug and send out an RFR.

Thanks!

/Claes