-[WKView _updateWindowAndViewFrames] should avoid updating the view frame in window coordinates if we don't have plugins
https://bugs.webkit.org/show_bug.cgi?id=117420
<rdar://problem/14073034>

Reviewed by Tim Horton.

If plug-ins are disabled there's no need for the web process to know about the view frame in window coordinates so only
send it when plug-ins are enabled. In addition, if accessibility is disabled we don't need to send a message at all.

* UIProcess/API/mac/PageClientImpl.h:
* UIProcess/API/mac/PageClientImpl.mm:
(WebKit::PageClientImpl::preferencesDidChange):
Call through to -[WKView _preferencesDidChange].

* UIProcess/API/mac/WKView.mm:
(-[WKView _updateWindowAndViewFrames]):
Don't compute viewFrameInWindowCoordinates or accessibilityPosition unless they're required. If neither are required,
don't even send a message to the web process.

(-[WKView _preferencesDidChange]):
Update _needsViewFrameInWindowCoordinates and call -[WKView _updateWindowAndViewFrames] if needed.

(-[WKView initWithFrame:contextRef:pageGroupRef:relatedToPage:]):
Set _needsViewFrameInWindowCoordinates based on whether plug-ins are enabled or not.

* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::preferencesDidChange):
Call the page client.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@151403 268f45cc-cd09-0410-ab3c-d52691b4dbfc