The AstGraphBuilder is used for asm.js only and for-in is not allowed in
valid asm.js, so we can just disable optimization for asm.js functions
that contain for-in loops. This way we only need to support for-in via
the BytecodeGraphBuilder in TurboFan now, which will make optimizations
way easier.

R=yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2679913004
Cr-Commit-Position: refs/heads/master@{#43024}