Extract CSA::HandleLoadICSmiHandlerCase() from CSA::HandleLoadICHandlerCase() and
CSA::EmitLoadICProtoArrayCheck() from CSA::HandleLoadICProtoHandler().

This is a preliminary step for extracting LoadICProtoArrayCheck to a separate stub
which is necesary to fix the preformance regression caused by proto array
handlers support.

BUG=v8:5561, chromium:660795

Review-Url: https://codereview.chromium.org/2498013002
Cr-Commit-Position: refs/heads/master@{#40983}