Port 28e3467a72 (r38361)
original commit message:
Adding new methods to the code stub assembler and interpreter
assembler to combine loading and untagging SMIs, so that on 64-bit
architectures we can avoid loading the full 64 bits and load the
32 interesting bits directly instead.
BUG=
Review-Url: https://codereview.chromium.org/2265043002
Cr-Commit-Position: refs/heads/master@{#38811}
239f981653