Port f6e689ce

Original commit message:
    The TruncateFloat64ToUint64 operator converts a float64 to an uint64 using
    round-to-zero rounding mode (truncate). If the input value is outside uint64
    range, then the result depends on the architecture.

R=ahaas@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1460093002

Cr-Commit-Position: refs/heads/master@{#32181}