Optimize InjectorBuilder.build() and getJustInTimeBinding() for child injectors.

_From [crazyboblee](https://code.google.com/u/114815478402472606661/) on July 30, 2010 13:30:39_

Sam Pullara provided the attached trace. The total response time is 16ms, so we're pretty fast already, but we may be able to go faster.

We should be able to create child injectors with high frequency and concurrency.

**Binary attachments:** [Screen shot 2010-07-30 at 10.12.09 AM.png](http://code.google.com/p/google-guice/issues/detail?id=529)

_Original issue: http://code.google.com/p/google-guice/issues/detail?id=529_