Build fixes for GCC-using ports after r159965 and later

Build fixes for GCC-using ports after r159965 and later
https://bugs.webkit.org/show_bug.cgi?id=125136

GCC doesn't process API::ClientTraits template instantiations unless they're done
inside the API namespace.

* Shared/WebConnectionClient.h:
* UIProcess/Notifications/WebNotificationProvider.h:
* UIProcess/WebContextClient.h:
* UIProcess/WebContextConnectionClient.h:
* UIProcess/WebContextInjectedBundleClient.h:
* UIProcess/WebCookieManagerProxyClient.h:
* UIProcess/WebDatabaseManagerProxyClient.h:
* UIProcess/WebDownloadClient.h:
* UIProcess/WebFindClient.h:
* UIProcess/WebFormClient.h:
* UIProcess/WebGeolocationProvider.h:
* UIProcess/WebHistoryClient.h:
* UIProcess/WebIconDatabaseClient.h:
* UIProcess/WebLoaderClient.h:
* UIProcess/WebOriginDataManagerProxyChangeClient.h:
* UIProcess/WebPageContextMenuClient.h:
* UIProcess/WebPolicyClient.h:
* UIProcess/WebUIClient.h:
* WebProcess/InjectedBundle/InjectedBundleClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageContextMenuClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageDiagnosticLoggingClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageEditorClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageFormClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageFullScreenClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageLoaderClient.h:
* WebProcess/InjectedBundle/InjectedBundlePagePolicyClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageResourceLoadClient.h:
* WebProcess/InjectedBundle/InjectedBundlePageUIClient.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@159994 268f45cc-cd09-0410-ab3c-d52691b4dbfc