Fix crash in MemoryCache::replace.

Fix crash in MemoryCache::replace.

It's possible that MemoryCache::replace will try to evict a resource that has
already been evicted. If there is another resource present in its place, it
won't get evicted, but will get partially overwritten. In that partial
overwrite, we leave references to it in the LRU lists, leading to later
crashes.

BUG=357174
TEST=MemoryCacheTest.RemoveDuringRevalidation

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=170217

[abarth-chromium, 2014-03-27 21:05:19]

LGTM

yay for unit tests

[Nate Chapin, 2014-03-27 21:08:22]

On 2014/03/27 21:05:19, abarth wrote:
> LGTM
> 
> yay for unit tests

I know, right?

[Nate Chapin, 2014-03-27 21:08:26]

The CQ bit was checked by japhet@chromium.org

[commit-bot: I haz the power, 2014-03-27 21:09:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/japhet@chromium.org/214773004/1

[commit-bot: I haz the power, 2014-03-27 21:26:10]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-03-27 21:26:11]

Try jobs failed on following builders:
  tryserver.blink on win_blink_compile_dbg

[Nate Chapin, 2014-03-27 21:33:17]

The CQ bit was checked by japhet@chromium.org

[commit-bot: I haz the power, 2014-03-27 21:33:27]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/japhet@chromium.org/214773004/1

[commit-bot: I haz the power, 2014-03-27 22:33:05]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-03-27 22:33:06]

Commit queue rejected this change because the description was changed
between the time the change entered the commit queue and the time it
was ready to commit. You can safely check the commit box again.

[Nate Chapin, 2014-03-27 22:59:43]

The CQ bit was checked by japhet@chromium.org

[commit-bot: I haz the power, 2014-03-27 22:59:49]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/japhet@chromium.org/214773004/1

[commit-bot: I haz the power, 2014-03-27 23:00:19]

Change committed as 170217