Replace StringImpl* callback parameters with const String&
https://bugs.webkit.org/show_bug.cgi?id=133922

Reviewed by Sam Weinig.

* UIProcess/API/C/WKPage.cpp:
(toGenericCallbackFunction): Added this helper function to wrap a WKStringRef-returning
API callback in a generic const String&-returning callback.
(WKPageRenderTreeExternalRepresentation):
(WKPageGetSourceForFrame):
(WKPageGetContentsAsString):
(WKPageGetBytecodeProfile):
(WKPageValidateCommand):
* UIProcess/API/mac/WKView.mm:
(-[WKView validateUserInterfaceItem:]):
(-[WKView startSpeaking:]):
* UIProcess/WebPageProxy.h:
* UIProcess/ios/WKContentViewInteraction.mm:
(-[WKContentView _define:]):
(-[WKContentView applyAutocorrection:toString:withCompletionHandler:]):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@169987 268f45cc-cd09-0410-ab3c-d52691b4dbfc