A startup snapshot is considered cold when it does not contain any
function code. We can now create a warm startup snapshot from a cold one
by running a warm-up script. Functions exercised by the warm-up script
are compiled and its code included in the warm startup snapshot. Side
effects caused by the warm-up script does not persist.

R=vogelheim@chromium.org
BUG=v8:4836
LOG=Y

Review URL: https://codereview.chromium.org/1805903002

Cr-Commit-Position: refs/heads/master@{#34849}