[turbofan] Reduce context accesses during typed lowering.

src/compiler/access-builder.h

Index: src/compiler/access-builder.h
diff --git a/src/compiler/access-builder.h b/src/compiler/access-builder.h
index 4c22efa6ff3f07cd5a564153f64a4fb0f960591e..d6385e444dc87bc86d36157a92222fe6590622c7 100644
--- a/src/compiler/access-builder.h
+++ b/src/compiler/access-builder.h
@@ -43,6 +43,9 @@ class AccessBuilder FINAL : public AllStatic {
   // Provides access to JSValue::value() field.
   static FieldAccess ForValue();
 
+  // Provides access Context slots.
+  static FieldAccess ForContextSlot(size_t index);
+
   // Provides access to FixedArray elements.
   static ElementAccess ForFixedArrayElement();