[GTK] Add padding to all public class structs for future expansion without breaking ABI
https://bugs.webkit.org/show_bug.cgi?id=112565

Reviewed by Anders Carlsson.

Use 4 pointers for most of the classes that are unlikely to grow
and 8 for WebKitWebView and WebKitWebContext.

* UIProcess/API/gtk/WebKitBackForwardList.h:
(_WebKitBackForwardListClass):
* UIProcess/API/gtk/WebKitBackForwardListItem.h:
(_WebKitBackForwardListItemClass):
* UIProcess/API/gtk/WebKitContextMenu.h:
(_WebKitContextMenuClass):
* UIProcess/API/gtk/WebKitContextMenuItem.h:
(_WebKitContextMenuItemClass):
* UIProcess/API/gtk/WebKitCookieManager.h:
(_WebKitCookieManagerClass):
* UIProcess/API/gtk/WebKitDownload.h:
(_WebKitDownloadClass):
* UIProcess/API/gtk/WebKitFaviconDatabase.h:
(_WebKitFaviconDatabaseClass):
* UIProcess/API/gtk/WebKitFileChooserRequest.h:
(_WebKitFileChooserRequestClass):
* UIProcess/API/gtk/WebKitFindController.h:
(_WebKitFindControllerClass):
* UIProcess/API/gtk/WebKitFormSubmissionRequest.h:
(_WebKitFormSubmissionRequestClass):
* UIProcess/API/gtk/WebKitGeolocationPermissionRequest.h:
(_WebKitGeolocationPermissionRequestClass):
* UIProcess/API/gtk/WebKitHitTestResult.h:
(_WebKitHitTestResultClass):
* UIProcess/API/gtk/WebKitNavigationPolicyDecision.h:
(_WebKitNavigationPolicyDecisionClass):
* UIProcess/API/gtk/WebKitPlugin.h:
(_WebKitPluginClass):
* UIProcess/API/gtk/WebKitPolicyDecision.h:
(_WebKitPolicyDecisionClass):
* UIProcess/API/gtk/WebKitPrintOperation.h:
(_WebKitPrintOperationClass):
* UIProcess/API/gtk/WebKitResponsePolicyDecision.h:
(_WebKitResponsePolicyDecisionClass):
* UIProcess/API/gtk/WebKitSecurityManager.h:
(_WebKitSecurityManagerClass):
* UIProcess/API/gtk/WebKitSettings.h:
(_WebKitSettingsClass):
* UIProcess/API/gtk/WebKitURIRequest.h:
(_WebKitURIRequestClass):
* UIProcess/API/gtk/WebKitURIResponse.h:
(_WebKitURIResponseClass):
* UIProcess/API/gtk/WebKitURISchemeRequest.h:
(_WebKitURISchemeRequestClass):
* UIProcess/API/gtk/WebKitWebContext.h:
(_WebKitWebContextClass):
* UIProcess/API/gtk/WebKitWebInspector.h:
(_WebKitWebInspectorClass):
* UIProcess/API/gtk/WebKitWebResource.h:
(_WebKitWebResourceClass):
* UIProcess/API/gtk/WebKitWebView.h:
(_WebKitWebViewClass):
* UIProcess/API/gtk/WebKitWebViewBase.h:
(_WebKitWebViewBaseClass):
* UIProcess/API/gtk/WebKitWebViewGroup.h:
(_WebKitWebViewGroupClass):
* UIProcess/API/gtk/WebKitWindowProperties.h:
(_WebKitWindowPropertiesClass):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150130 268f45cc-cd09-0410-ab3c-d52691b4dbfc