Split HPhase for Lithium and Hydrogen using common CompilationPhase base.

Add new base class CompilationPhase, which is the base for both HPhase, LPhase and LAllocatorPhase. HPhase is now for Hydrogen passes only, LPhase is for Lithium passes and LAllocatorPhase is for LAllocator phases.

R=svenpanne@chromium.org
BUG=

Review URL: https://codereview.chromium.org/17572011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15321 ce2b1a6d-e550-0410-aec6-3dcde31c8c00