Add spread rewriting

src/ast/ast.h

Index: src/ast/ast.h
diff --git a/src/ast/ast.h b/src/ast/ast.h
index 7f00955a644fcaeeeca1be192c67a5afa7ec0b70..54b5c4eca782ff616259a0bcce409b46dcf6fa0e 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -1683,6 +1683,19 @@ class ArrayLiteral final : public MaterializedLiteral {
     return flags;
   }
 
+  // Provide a mechanism for iterating through values to rewrite spreads.
+  ZoneList<Expression*>::iterator FirstSpread() const {
+    return (first_spread_index_ >= 0) ? values_->begin() + first_spread_index_
+                                      : values_->end();
+  }
+  ZoneList<Expression*>::iterator EndValue() const { return values_->end(); }
+
+  // Rewind an array literal omitting everything from the first spread on.
+  void RewindSpreads() {
+    values_->Rewind(first_spread_index_);
+    first_spread_index_ = -1;
+  }
+
   enum Flags {
     kNoFlags = 0,
     kShallowElements = 1,