Fix ExtensionPopup close issue.

Fix chrome.extension.getViews returns multiple popup windows.

When we invoke +[ExtensionPopupController showURL:...],
we close the old Popup using [gPopup close],but we don't
release it here. So host_ is only released 
when -[ExtensionPopupController windowWillClose] is invoked.
At this time, the new popup might be ready. And when we use
chrome.extension.getViews or some other apis we might get
the dying window.
So move shutdown of host_ from -[ExtensionPopupController windowWillClose]
into -[ExtensionPopupController close].

BUG=376511
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=276355

[Xuefei Ren, 2014-06-10 05:24:32]

Add some comments about why I do this.

https://codereview.chromium.org/321093002/diff/1/chrome/browser/ui/cocoa/exte...
File chrome/browser/ui/cocoa/extensions/extension_popup_controller.mm (right):

https://codereview.chromium.org/321093002/diff/1/chrome/browser/ui/cocoa/exte...
chrome/browser/ui/cocoa/extensions/extension_popup_controller.mm:291: [gPopup
close];
See bug:361278, and patch is 64ced6a2af4cb2b46756bc60515c6eaed2f5c428
There was a [gPopup autorelease].
We used to release extension::ExtensionViewHost host_ by this autorelease to
dealloc ExtensionViewHost.
Now we only can use -[ExtensionPopupController windowWillClose] to 
close the host_.
This will cause new popup is ready but the old one is still alive.
Then we use chrome.extension.getViews we will get more views.
So make sure that when we [gPopup close] the old one will truely shutdown the
host_.

[Mark Mentovai, 2014-06-10 21:15:15]

LGTM

[Xuefei Ren, 2014-06-11 00:57:41]

The CQ bit was checked by xrenishere@gmail.com

[commit-bot: I haz the power, 2014-06-11 01:02:05]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/xrenishere@gmail.com/321093002/1

[commit-bot: I haz the power, 2014-06-11 11:49:50]

Change committed as 276355

[Xuefei Ren, 2014-07-02 06:07:10]

A revert of this CL has been created in
https://codereview.chromium.org/364783003/ by xrenishere@gmail.com.

The reason for reverting is: Have to revert this. There is some cases such as
when in extension open a new tab with window.open or  a link, this will crash
the browser.See bug 390128..