[stubs] Port LoadScriptContextFieldStub and StoreScriptContextFieldStub to TurboFan.

src/code-stub-assembler.h

Index: src/code-stub-assembler.h
diff --git a/src/code-stub-assembler.h b/src/code-stub-assembler.h
index b14a6b0c1c1e80bd6aafab21e3d6bbabb3d9e354..d34f58c4854681062a2afb882b9eaaf3590182b7 100644
--- a/src/code-stub-assembler.h
+++ b/src/code-stub-assembler.h
@@ -274,6 +274,7 @@ class CodeStubAssembler : public compiler::CodeAssembler {
       MachineType machine_type = MachineType::Float64());
 
   // Context manipulation
+  compiler::Node* LoadContextElement(compiler::Node* context, int slot_index);
   compiler::Node* LoadNativeContext(compiler::Node* context);
 
   compiler::Node* LoadJSArrayElementsMap(ElementsKind kind,
@@ -658,6 +659,9 @@ class CodeStubAssembler : public compiler::CodeAssembler {
     EmitKeyedSloppyArguments(receiver, key, value, bailout);
   }
 
+  // Loads script context from the script context table.
+  compiler::Node* LoadScriptContext(compiler::Node* context, int context_index);
+
   void LoadIC(const LoadICParameters* p);
   void LoadGlobalIC(const LoadICParameters* p);
   void KeyedLoadIC(const LoadICParameters* p);