RFR(S): 8135076: Preparatory refactorings for compiler control

[Nils Eliasson]

Hi all,

This patch contains only independent minor refactorings that has been 
split out for the compiler control repo. (To make that change more 
manageable).
  - Extract CompileTask from CompileBroker into separate files. (Code 
the same except for some method name adjustments for a more consistent 
experience.)
  - Removal of several unnecessary includes

bug: https://bugs.openjdk.java.net/browse/JDK-8135067
webrev: http://cr.openjdk.java.net/~neliasso/8135067/webrev.01/

Regular testing applied.

Please review,
Nils