Fixed <rdar://problem/5091330> REGRESSION: Repro crash in 
        -[WebBaseNetscapePluginView(WebNPPCallbacks) destroyStream:reason:] 
        navigating away from page with DivX movie plug-in (13203)
        
        The problem was that the DivX plug-in would ask us to destroy an NPStream
        that had already been destroyed, causing us to wander off into freed
        memory. (I believe the reason this was a regression was that we never used 
        to destroy plug-in streams, period.)
        
        The solution here is to track the NPStreams belonging to a plug-in, and 
        guard against plug-ins making calls with NPStreams that don't belong to 
        them. (It turns out that NPN_DestroyStream is the only stream-based 
        plug-in call we support.)

        (CarbonPathFromPOSIXPath): Fixed up a cast to be C++ compatible.
        * Plugins/WebBaseNetscapePluginView.mm:
        (-[WebBaseNetscapePluginView destroyStream:reason:]): The actual fix.
        Use helper method to guard against a plug-in using an NPStream that doesn't
        belong to it.
        * WebKit.xcodeproj/project.pbxproj: Made WebBaseNetscapePluginView ObjC++
        so I could use HashMap.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20571 268f45cc-cd09-0410-ab3c-d52691b4dbfc