Reviewed by Maciej Stachowiak.
        
        Removed dynamic check for whether the callee needs an activation object.
        Replaced with callee code to create the activation object.

        0.5% speedup on SunSpider.
        No change on v8 benchmark. (Might be a speedup, but it's in range of the
        variance.)

        0.7% speedup on v8 benchmark in bytecode.
        1.3% speedup on empty call benchmark in bytecode.

        * VM/CTI.cpp:
        (JSC::CTI::privateCompileMainPass): Added support for op_init_activation,
        the new opcode that specifies that the callee's initialization should
        create an activation object.
        (JSC::CTI::privateCompile): Removed previous code that did a similar
        thing in an ad-hoc way.

        * VM/CodeBlock.cpp:
        (JSC::CodeBlock::dump): Added a case for dumping op_init_activation.

        * VM/CodeGenerator.cpp:
        (JSC::CodeGenerator::generate): Added fixup code to change op_init to
        op_init_activation if necessary. (With a better parser, we would know
        which to use from the beginning.)

        * VM/Instruction.h:
        (JSC::Instruction::Instruction):
        (WTF::): Faster traits for the instruction vector. An earlier version
        of this patch relied on inserting at the beginning of the vector, and
        depended on this change for speed.

        * VM/Machine.cpp:
        (JSC::Machine::execute): Removed clients of setScopeChain, the old
        abstraction for dynamically checking for whether an activation object
        needed to be created.
        (JSC::Machine::privateExecute): ditto

        (JSC::Machine::cti_op_push_activation): Renamed this function from
        cti_vm_updateScopeChain, and made it faster by removing the call to 
        setScopeChain.
        * VM/Machine.h:

        * VM/Opcode.h: Declared op_init_activation.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@36972 268f45cc-cd09-0410-ab3c-d52691b4dbfc