Fix weak processing over cleared hash tables.
When a hash table of weak references is traced during the GC
marking phase, a weak callback is registered for processing after
that initial marking pass.
The hash table may be populated with entries at the time when
that weak callback is registered, but may end up being cleared
before the weak callback actually gets to run.
Account for that latter possibility by having the weak callback
being invoked first gracefully check if the backing table exists
before proceeding to process it.
R=haraken
BUG=549732
NOTRY=true
Review URL: https://codereview.chromium.org/1410373006
Cr-Commit-Position: refs/heads/master@{#357282}
1 file changed
