Now that we keep tabs on shared function infos from a script, we can speed up finding shared function infos for debugging. However, in case we have to compile a function that cannot be lazily compiled without context, we fall back to the slow heap iteration.

R=mstarzinger@chromium.org
BUG=v8:4132,v8:4052
LOG=N

Review URL: https://codereview.chromium.org/1206573004

Cr-Commit-Position: refs/heads/master@{#29296}