https://bugs.webkit.org/show_bug.cgi?id=125104

Reviewed by Sam Weinig.

Add multiple versions of the WKPageLoaderClient struct. In a subsequent patch,
WKPageLoaderClient and kWKPageLoaderClientCurrentVersion will be deprecated. Instead,
users of the API are supposed to explicitly choose a version and a versioned struct.

* Shared/APIClient.h:
Add a new API::Client class with a new ClientTraits template that uses std::tuple for versions.

* Shared/APIClientTraits.cpp:
* Shared/APIClientTraits.h:
Remove WKPageLoaderClient interface sizes.

* UIProcess/API/C/WKPage.cpp:
(WKPageSetPageLoaderClient):
Add an explicit cast to WKPageLoaderClientBase. In an upcoming patch, WKPageSetPageLoaderClient
will be changed to take a WKPageLoaderClientBase instead.

* UIProcess/API/C/WKPageLoaderClient.h:
Add new versions.

* UIProcess/API/Cocoa/WKBrowsingContextController.mm:
(setUpPageLoaderClient):
Use an explicit version.

* UIProcess/WebLoaderClient.cpp:
(WebKit::WebLoaderClient::didStartProvisionalLoadForFrame):
(WebKit::WebLoaderClient::didReceiveServerRedirectForProvisionalLoadForFrame):
(WebKit::WebLoaderClient::didFailProvisionalLoadWithErrorForFrame):
(WebKit::WebLoaderClient::didCommitLoadForFrame):
(WebKit::WebLoaderClient::didFinishDocumentLoadForFrame):
(WebKit::WebLoaderClient::didFinishLoadForFrame):
(WebKit::WebLoaderClient::didFailLoadWithErrorForFrame):
(WebKit::WebLoaderClient::didSameDocumentNavigationForFrame):
(WebKit::WebLoaderClient::didReceiveTitleForFrame):
(WebKit::WebLoaderClient::didFirstLayoutForFrame):
(WebKit::WebLoaderClient::didFirstVisuallyNonEmptyLayoutForFrame):
(WebKit::WebLoaderClient::didLayout):
(WebKit::WebLoaderClient::didRemoveFrameFromHierarchy):
(WebKit::WebLoaderClient::didDisplayInsecureContentForFrame):
(WebKit::WebLoaderClient::didRunInsecureContentForFrame):
(WebKit::WebLoaderClient::didDetectXSSForFrame):
(WebKit::WebLoaderClient::canAuthenticateAgainstProtectionSpaceInFrame):
(WebKit::WebLoaderClient::didReceiveAuthenticationChallengeInFrame):
(WebKit::WebLoaderClient::didStartProgress):
(WebKit::WebLoaderClient::didChangeProgress):
(WebKit::WebLoaderClient::didFinishProgress):
(WebKit::WebLoaderClient::processDidBecomeUnresponsive):
(WebKit::WebLoaderClient::interactionOccurredWhileProcessUnresponsive):
(WebKit::WebLoaderClient::processDidBecomeResponsive):
(WebKit::WebLoaderClient::processDidCrash):
(WebKit::WebLoaderClient::didChangeBackForwardList):
(WebKit::WebLoaderClient::shouldGoToBackForwardListItem):
(WebKit::WebLoaderClient::willGoToBackForwardListItem):
(WebKit::WebLoaderClient::didFailToInitializePlugin):
(WebKit::WebLoaderClient::didBlockInsecurePluginVersion):
(WebKit::WebLoaderClient::pluginLoadPolicy):
Go through client.base everywhere.

* UIProcess/WebLoaderClient.h:
Add API::ClientTraits specialization. Change WebLoaderClient to derive from API::Client<WKPageLoaderClientBase>.

* UIProcess/WebPageProxy.cpp:
(WebKit::WebPageProxy::initializeLoaderClient):
This now takes a WKPageLoaderClientBase*.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@159965 268f45cc-cd09-0410-ab3c-d52691b4dbfc