Cursor doesn't change back to pointer when leaving the Safari window

Cursor doesn't change back to pointer when leaving the Safari window
https://bugs.webkit.org/show_bug.cgi?id=132038

Reviewed by Alexey Proskuryakov.

Source/WebCore:
r147739 incorrectly added an early exit in EventHandler::selectCursor when hit test result didn't have
any node associated with it. Since we will hit this code when the cursor is outside of the WebView,
we still need to take the CURSOR_AUTO path as did the code before r147739.

No new test is added since this behavior can't be tested in DRT or WTR.

* page/EventHandler.cpp:
(WebCore::EventHandler::selectCursor):

Source/WebKit/mac:
Since the cursor type is now updated asynchronously after r147739,
[window windowNumber] != [NSWindow windowNumberAtPoint:[NSEvent mouseLocation] belowWindowWithWindowNumber:0]
evalutes to false depending on how fast cursor is moving.

Instead, check whether the NSWindow of the WebView is the key window or not since
key window appears to control the cursor style in Cocoa as far as I've tested:
https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/WinPanel/Concepts/ChangingMainKeyWindow.html

* WebCoreSupport/WebChromeClient.mm:
(WebChromeClient::setCursor):

Source/WebKit2:
Since the cursor type is now updated asynchronously after r147739,
[window windowNumber] != [NSWindow windowNumberAtPoint:[NSEvent mouseLocation] belowWindowWithWindowNumber:0]
evalutes to false depending on how fast cursor is moving.

Instead, check whether the NSWindow of the WebView is the key window or not since
key window appears to control the cursor style in Cocoa as far as I've tested:
https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/WinPanel/Concepts/ChangingMainKeyWindow.html

* UIProcess/mac/PageClientImpl.mm:
(WebKit::PageClientImpl::setCursor):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167700 268f45cc-cd09-0410-ab3c-d52691b4dbfc