<webview>: Speculative fix

<webview>: Speculative fix

I'm fairly confident this is the fix to bug 343383. From the stack traces,
it appears that during ChildFrameCompositorHelper destruction, DelegatedFrameProvider
is destroyed which accesses ChildFrameCompositingHelper::SendReclaimCompositorResourcesToBrowser.
That method accesses the BrowserPlugin weak pointer which is destroyed prior to
DelegatedFrameProvider's destruction. This change ensures that the weak pointer is the last
of the non-primitive members of ChildFrameCompositingHelper to get destroyed.

BUG=343383
TBR=nasko@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=251710

[Fady Samuel, 2014-02-17 16:46:51]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2014-02-17 16:47:15]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/fsamuel@chromium.org/169653004/1

[commit-bot: I haz the power, 2014-02-17 17:08:47]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-02-17 17:08:48]

Try jobs failed on following builders: linux_chromium_rel

[Fady Samuel, 2014-02-17 18:09:36]

The CQ bit was checked by fsamuel@chromium.org

[Fady Samuel, 2014-02-17 18:09:37]

The CQ bit was unchecked by fsamuel@chromium.org

[Fady Samuel, 2014-02-17 18:09:38]

The CQ bit was checked by fsamuel@chromium.org

[commit-bot: I haz the power, 2014-02-17 18:09:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/fsamuel@chromium.org/169653004/290001

[commit-bot: I haz the power, 2014-02-18 00:38:00]

Change committed as 251710