- fixed <rdar://problem/5138492> Safari doesn't remember some changes to the PDF scale and display mode 

        Some of the user interactions that could change the PDF scale and display mode were not going through
        the proxy mechanism in WebPDFView that updates preferences. Now we also listen to PDFKit notifications
        in order to catch the other cases.

        * WebView/WebPDFView.h:
        new _ignoreScaleAndDisplayModeNotifications and _updatePreferencesTimer ivars

        * WebView/WebPDFView.mm:
        (-[WebPDFView setPDFDocument:]):
        ignore scale and display mode notifications while we're setting up a fresh document
        (-[WebPDFView dealloc]):
        cancel the new timer (which releases it)
        (-[WebPDFView viewDidMoveToWindow]):
        listen for two PDFKit notifications
        (-[WebPDFView viewWillMoveToWindow:]):
        stop listening to the two PDFKit notifications
        (-[WebPDFView _applyPDFDefaults]):
        white space change
        (-[WebPDFView _cancelUpdatePreferencesTimer]):
        invalidate, release, and nil out the timer
        (-[WebPDFView _scaleOrDisplayModeChanged:]):
        update preferences soon, unless deliberately ignoring these notifications
        (-[WebPDFView _updatePreferencesNow]):
        cancel timer, then save data to preferences (code for saving the data was extracted from
        -[PDFPrefUpdatingProxy forwardInvocation:])
        (-[WebPDFView _updatePreferencesSoon]):
        use timer to consolidate multiple calls into one action; formerly we were setting preferences
        multiple times for some atomic user actions
        (-[PDFPrefUpdatingProxy forwardInvocation:]):
        call _updatePreferencesSoon where we used to immediately set preferences



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20924 268f45cc-cd09-0410-ab3c-d52691b4dbfc