Reviewed by Geoff Garen.

        Sampling tool to analyze cost of instruction execution and identify hot regions of JS code.
        Enable Switches by setting SAMPLING_TOOL_ENABLED in Opcode.h.

        * JavaScriptCore.exp: Export symbols for Shell.cpp.
        * VM/Machine.cpp:     Added sampling hooks.
        * VM/Machine.h:       Machine contains a pointer to a sampler, when sampling.
        * VM/Opcode.cpp:      Tool implementation.
        * VM/Opcode.h:        Tool declaration.
        * kjs/Shell.cpp:      Initialize the sampler, if enabled.
        * kjs/nodes.cpp:      Added sampling hooks.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@35305 268f45cc-cd09-0410-ab3c-d52691b4dbfc