[Isolates] Fix the crash in AssertNoContextChange ctor when current context i...

[Isolates] Fix the crash in AssertNoContextChange ctor when current context is NULL.

Committed: http://code.google.com/p/v8/source/detail?r=7249

[Dmitry Titov, 2011-03-17 03:40:23]

I'm getting a crash that I am not sure how to fix better. Attaching a patch, but
here is more info, please advise:

Here is what happens:

1. Test 1 loads and works perfectly.
2. Test 2 is loading after Test 1, this causes Test 1's document to be unloaded.
3. While unloading Test 1, WebCore Releases EventListeners and some cleanup
happens on V8 side
4. V8 crashes because at this point there is no Context - no Context was
entered. It worked before because we didn't try to use HeapObject::GetIsolate()
on a NULL, and now we do.

Here is log with crash stack:
http://build.chromium.org/p/tryserver.chromium/builders/win_layout/builds/564...,
search for "Stacktrace for svg/carto.net/colourpicker.svg". 
It crashes because in AssertNoContextChange ctor the context is actually NULL
and we try to create the Handle<Context>, which tries to pull isolate from that
NULL.

I don't know if creating a Handle from NULL is a valid scenario. Or if
GetProperty should always happen in som econtext. If not, then we have to make
sure we enter some context on that callstack.

Separately, I think we should only have Handle<> ctor that takes Isolate (or
HandleScope) - and then remove the code that currently tries to pull Isolate if
an argument is a HeapObject.

WDYT?

[Dmitry Titov, 2011-03-17 03:42:35]

To repro the crash, one need to run more then one test from that dir, like this:
python webkit\tools\layout_tests\run_webkit_tests.py --debug svg/carto.net

[Vitaly Repeshko, 2011-03-17 18:13:42]

LGTM (with comments) as a quick fix.

Anton is probably right that we should change the listener implementation, but
it would be a way more risky change.

http://codereview.chromium.org/6665063/diff/1/src/isolate.h
File src/isolate.h (right):

http://codereview.chromium.org/6665063/diff/1/src/isolate.h#newcode1183
src/isolate.h:1183: isolate_(Isolate::Current()),
Convert tabs to spaces.

http://codereview.chromium.org/6665063/diff/1/src/isolate.h#newcode1185
src/isolate.h:1185: context_(isolate_->context(), isolate_) {
Just pass Isolate::Current(). No need to save it in a field.

[Dmitry Titov, 2011-03-17 20:19:08]

Thanks!

Fixed as suggested and landed.