[ic] Refactor LoadIC code.

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}

src/code-stub-assembler.h

@@ -1144,11 +1144,22 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
       const LoadICParameters* p, compiler::Node* handler, Label* miss,
       ElementSupport support_elements = kOnlyProperties);
 
+  void HandleLoadICSmiHandlerCase(const LoadICParameters* p,
+                                  compiler::Node* holder,
+                                  compiler::Node* smi_handler, Label* miss,
+                                  ElementSupport support_elements);
+
   void HandleLoadICProtoHandler(const LoadICParameters* p,
                                 compiler::Node* handler, Variable* var_holder,
                                 Variable* var_smi_handler,
                                 Label* if_smi_handler, Label* miss);
 
+  compiler::Node* EmitLoadICProtoArrayCheck(const LoadICParameters* p,
+                                            compiler::Node* handler,
+                                            compiler::Node* handler_length,
+                                            compiler::Node* handler_flags,
+                                            Label* miss);
+
   void CheckPrototype(compiler::Node* prototype_cell, compiler::Node* name,
                       Label* miss);