Fix a crash when built with 10.7 SDK running on OS X 10.6

Fix a crash when built with 10.7 SDK running on OS X 10.6

NSWindowDidChangeBackingPropertiesNotification is available since 10.7.

Our buildbots use OS X 10.7 SDK to build with minimum target system
version set to 10.6. For features available only to 10.7 and up, we
normally have runtime guard to check if the system is 10.6 then we don't
use it.

However this one is in chromium content module and it doesn't have such
runtime check. We don't know the exact details of chromium buildbot or
how do they make release builds, it seems that they are building 10.6
releases with 10.6 SDK (which will disable the feature in compile time).

BUG=260595
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=212060

[Jiang Jiang, 2013-07-11 10:27:02]

Hi, it might be a Opera specific issue (since we built 10.6 builds with 10.7
SDK) but the only possible fix is in Chromium so we want to upstream this.

[Nico, 2013-07-11 22:13:33]

Hi Jiang,

our bots build with the 10.6 SDK, which is probably why we don't see this. But
we're very interested in patches that make chrome built with newer sdks run well
on 10.6, so thanks for this :-)

I don't understand why this would crash however. Shouldn't add/removeObserver:
just ignore names it doesn't know about? It seems to do that successfully when
built with the 10.6 sdk. I suppose the 10.7 sdk implementation of this is buggy
and assumes that the os is 10.7+? What's the stack for this?

[Jiang Jiang, 2013-07-12 08:39:01]

On 2013/07/11 22:13:33, Nico wrote:
> Hi Jiang,
> 
> our bots build with the 10.6 SDK, which is probably why we don't see this. But
> we're very interested in patches that make chrome built with newer sdks run
well
> on 10.6, so thanks for this :-)
> 
> I don't understand why this would crash however. Shouldn't add/removeObserver:
> just ignore names it doesn't know about? It seems to do that successfully when
> built with the 10.6 sdk. I suppose the 10.7 sdk implementation of this is
buggy
> and assumes that the os is 10.7+? What's the stack for this?

Hi Nico, here is the stacktrace we got: https://gist.github.com/jjgod/5982852

[Nico, 2013-07-15 17:10:45]

On 2013/07/12 08:39:01, Jiang wrote:
> On 2013/07/11 22:13:33, Nico wrote:
> > Hi Jiang,
> > 
> > our bots build with the 10.6 SDK, which is probably why we don't see this.
But
> > we're very interested in patches that make chrome built with newer sdks run
> well
> > on 10.6, so thanks for this :-)
> > 
> > I don't understand why this would crash however. Shouldn't
add/removeObserver:
> > just ignore names it doesn't know about? It seems to do that successfully
when
> > built with the 10.6 sdk. I suppose the 10.7 sdk implementation of this is
> buggy
> > and assumes that the os is 10.7+? What's the stack for this?
> 
> Hi Nico, here is the stacktrace we got: https://gist.github.com/jjgod/5982852

Can you paste that into a bug and reference it? Also mention what kind of crash
it is (sigsegv or sigbus or…) Also add a comment above the bug saying "//
Backing property notifications crash on 10.6 when building with the 10.7 sdk,
http://crbug.com/YOURBUG#".

With that, lgtm

[commit-bot: I haz the power, 2013-07-17 08:26:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jiangj@opera.com/18674005/6001

[commit-bot: I haz the power, 2013-07-17 16:35:33]

Change committed as 212060