PPC: Add a MathFloor stub generated with TurboFan

PPC: Add a MathFloor stub generated with TurboFan

Port abc35080b33cc31e47b9913e64ac99ec687c6b65

Original commit message:
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.

R=danno@chromium.org, dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1137033002

Cr-Commit-Position: refs/heads/master@{#28341}