Fix terrible interaction with code flushing.

Fix terrible interaction with code flushing.

This fixes a terrible interaction of code flushing and the clearing of
optimized code maps hanging off a SharedFunctionInfo. The following is
what happened:
1) Incremental marking cleared map in SharedFunctionInfo s, however it
   was not enqueued as a flushing candidate because one JSFunction f1
   still had optimized code.
2) Deoptimization of f1 made s eligible for code flushing.
3) Optimization of f2 added new entry to optimized code map of s.
4) The JSFunction f2 became unreachable and hence is never marked.
5) Incremental marking now visits f1, finds it eligible for flushing,
   also s is eligible for flushing, both are enqueued.
6) Marking finishes, code flusher clears f1 and s, but the optimized
   code map of s still contains an entry.
7) Boom!

R=ulan@chromium.org,hpayer@chromium.org
TEST=mjsunit/es6/generators-iteration
BUG=v8:3803
LOG=N

Committed: https://crrev.com/816abc5e864e503a5c9802483f555c339d7ac52f
Cr-Commit-Position: refs/heads/master@{#29177}

[Hannes Payer (out of office), 2015-06-19 19:21:28]

lgtm

[ulan, 2015-06-22 07:43:07]

On 2015/06/19 15:24:09, Michael Starzinger wrote:

lgtm!

[Michael Starzinger, 2015-06-22 08:03:44]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-06-22 08:03:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1197713004/20001

[commit-bot: I haz the power, 2015-06-22 08:25:38]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-22 08:25:58]

Patchset 2 (id:??) landed as
https://crrev.com/816abc5e864e503a5c9802483f555c339d7ac52f
Cr-Commit-Position: refs/heads/master@{#29177}

[wingo, 2015-06-22 09:06:33]

Michael you are amazing.  Thank you!!