[Interpreter] Add support for for..in.

src/compiler/interpreter-assembler.h

Index: src/compiler/interpreter-assembler.h
diff --git a/src/compiler/interpreter-assembler.h b/src/compiler/interpreter-assembler.h
index b546fb21f0526f1211e90ed927182e6632351ba9..abe98055c564354558ef5b50a88133791bceed76 100644
--- a/src/compiler/interpreter-assembler.h
+++ b/src/compiler/interpreter-assembler.h
@@ -92,6 +92,9 @@ class InterpreterAssembler {
   // Load constant at |index| in the constant pool.
   Node* LoadConstantPoolEntry(Node* index);
 
+  // Load an element from a fixed array on the heap.
+  Node* LoadFixedArrayElement(Node* fixed_array, int index);
+
   // Load a field from an object on the heap.
   Node* LoadObjectField(Node* object, int offset);