Convert ToBooleanStub to a HydrogenStub. Currently just using the existing HBranch instruction, which is still fully implemented in Lithium. Will refactor HBranch in a next CL.

[
CL breaks mips, since the deoptimizer in Deoptimizer::DoTranslateCommand(...) does not convert smis passed to the stub via a0.
]

BUG=
R=verwaest@chromium.org

Review URL: https://codereview.chromium.org/15302004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14886 ce2b1a6d-e550-0410-aec6-3dcde31c8c00