DelayedReleaseScope drops locks during GC which can cause a thread switch and code...

DelayedReleaseScope drops locks during GC which can cause a thread switch and code reentry
https://bugs.webkit.org/show_bug.cgi?id=141275

Reviewed by Geoffrey Garen.

The original issue is that the CodeCache uses an unsafe method to add new UnlinkedCodeBlocks.
It basically adds a null UnlinkedCodeBlock if there isn't a cached entry and then later
updates the null entry to the result of the compilation.  If during that compilation and
related processing we need to garbage collect, the DelayedReleaseScope would drop locks
possibly allowing another thread to try to get the same source out of the CodeCache.
This second thread would find the null entry and crash.  The fix is to move the processing of
DelayedReleaseScope to when we drop locks and not drop locks during GC.  That was done in
the original patch with the new function releaseDelayedReleasedObjects().

Updated releaseDelayedReleasedObjects() so that objects are released with all locks
dropped.  Now its processing follows these steps
    Increment recursion counter and do recursion check and exit if recursing
    While there are objects to release
        ASSERT that lock is held by current thread
        Take all items from delayed release Vector and put into temporary Vector
        Release API lock
        Release and clear items from temporary vector
        Reaquire API lock
This meets the requirement that we release while the API lock is released and it is
safer processing of the delayed release Vector.

Added new regression test to testapi.

Also added comment describing how recursion into releaseDelayedReleasedObjects() is
prevented.

* API/tests/Regress141275.h: Added.
* API/tests/Regress141275.mm: Added.
(+[JSTEvaluatorTask evaluatorTaskWithEvaluateBlock:completionHandler:]):
(-[JSTEvaluator init]):
(-[JSTEvaluator initWithScript:]):
(-[JSTEvaluator _accessPendingTasksWithBlock:]):
(-[JSTEvaluator insertSignPostWithCompletion:]):
(-[JSTEvaluator evaluateScript:completion:]):
(-[JSTEvaluator evaluateBlock:completion:]):
(-[JSTEvaluator waitForTasksDoneAndReportResults]):
(__JSTRunLoopSourceScheduleCallBack):
(__JSTRunLoopSourcePerformCallBack):
(__JSTRunLoopSourceCancelCallBack):
(-[JSTEvaluator _jsThreadMain]):
(-[JSTEvaluator _sourceScheduledOnRunLoop:]):
(-[JSTEvaluator _setupEvaluatorThreadContextIfNeeded]):
(-[JSTEvaluator _callCompletionHandler:ifNeededWithError:]):
(-[JSTEvaluator _sourcePerform]):
(-[JSTEvaluator _sourceCanceledOnRunLoop:]):
(runRegress141275):
* API/tests/testapi.mm:
(testObjectiveCAPI):
* JavaScriptCore.xcodeproj/project.pbxproj:
* heap/Heap.cpp:
(JSC::Heap::releaseDelayedReleasedObjects):
* runtime/JSLock.cpp:
(JSC::JSLock::unlock):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@180992 268f45cc-cd09-0410-ab3c-d52691b4dbfc