This stub will be used as the basis of a Math.floor-specific CallIC to
detect and track calls to floor that return -0.

Along the way:
- Create a TurboFanCodeStub super class from which the StringLength and
MathRound TF stubs derive.
- Fix the ugly hack that passes the first stub parameter as the "this"
pointer in the the TF-compiled JS function.
- Fix bugs in the ia32/x64 disassembler.

Review URL: https://codereview.chromium.org/1137703002

Cr-Commit-Position: refs/heads/master@{#28339}