Keep a canonical list of shared function infos.

Keep a canonical list of shared function infos.

Each Script object now keeps a WeakFixedArray of SharedFunctionInfo
objects created from this script.

This way, when compiling a function, we do not create duplicate shared
function info objects when recompiling with either compiler.

This fixes a class of issues in the debugger, where we set break points
on one shared function info, but functions from duplicate shared function
infos are not affected.

LOG=N
BUG=v8:4132

Review URL: https://codereview.chromium.org/1183733006

Cr-Commit-Position: refs/heads/master@{#29151}