Now that we have a JumpLoop bytecode, we can heavily simplify the
branch/loop analysis by assuming that only JumpLoop bytecodes are
backwards edges, and performing the loop analysis as a single
(backwards) pass.

This allows us to get rid of the branch analysis entirely, and builds a
framework to do liveness analysis in the same pass.

Review-Url: https://codereview.chromium.org/2519983002
Cr-Commit-Position: refs/heads/master@{#41194}