Reviewed by Maciej Stachowiak.

        Bug 21364: Remove the branch in op_ret for OptionalCalleeActivation and OptionalCalleeArguments
        <https://bugs.webkit.org/show_bug.cgi?id=21364>

        This patch does not yet remove the branch, but it does a bit of refactoring
        so that a CodeGenerator now knows whether the associated CodeBlock will need
        a full scope before doing any code generation. This makes it possible to emit
        explicit tear-off instructions before every op_ret.

        * VM/CodeBlock.h:
        (JSC::CodeBlock::CodeBlock):
        * VM/CodeGenerator.cpp:
        (JSC::CodeGenerator::generate):
        (JSC::CodeGenerator::CodeGenerator):
        (JSC::CodeGenerator::emitPushScope):
        (JSC::CodeGenerator::emitPushNewScope):
        * kjs/nodes.h:
        (JSC::ScopeNode::needsActivation):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@37320 268f45cc-cd09-0410-ab3c-d52691b4dbfc