Reading the registers' values back from the FrameDescription
should use the same offset computation as storing them into it.
The offsets must also match what the deoptimizer expects, which
is rx at offset rx.code() * kDoubleSize, even if some registers
are not saved (leaving gaps).
BUG=v8:4800
LOG=n
R=danno@chromium.org
Review URL: https://codereview.chromium.org/1769833006
Cr-Commit-Position: refs/heads/master@{#34633}
