Add null check in ChromeClientImpl::postAccessibilityNotification() for SharedWorker refactoring.

Add null check in ChromeClientImpl::postAccessibilityNotification().

Because AXObjectCache::accessibilityEnabled() always returns true in the shared worker process,
ChromeClientImpl::postAccessibilityNotification() is never called in the process.
So we don't need to check m_webView->client() now.

But we are planing to move SharedWorker to the renderer process.
http://crbug.com/327256
ChromeClientImpl::postAccessibilityNotification() will be called in the shared worker's WebFrame
when the accessibility feature is enabled.
But m_webView->client() is NULL in the shared worker's WebFrame.

So we have to check it.

BUG=327256
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=165606

[horo, 2014-01-17 08:51:31]

kinuko@
Could you please review this?

[kinuko, 2014-01-17 09:22:08]

Looks good/reasonable to me (I'd like to defer to owners)

[horo, 2014-01-17 09:25:06]

jamesr@
Please review this cl.

[horo, 2014-01-22 05:51:43]

adamk@
Can you take a look?
We need this tiny change.

Thank you.

[adamk, 2014-01-22 16:35:34]

lgtm

This seems fine; are there not other places that need added null-checks? From a
quick perusal of Source/web most callsites null-check their clients.

I'd ask for a test but I assume this isn't yet exercisable, but will be once
SharedWorkers move to the renderer.

[horo, 2014-01-23 01:00:44]

Thank you.

I think that other methods in which null pointer is not checked are not called
in the shared worker's WebFrame. 
I will do test when SharedWorkers move to the renderer.

[commit-bot: I haz the power, 2014-01-23 01:53:00]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/horo@chromium.org/134643019/1

[commit-bot: I haz the power, 2014-01-23 03:59:52]

Change committed as 165606