[es6] parse destructuring assignment

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 1366041387215bc4c018c4b1650d39ff5f6549c4..b497427bf228aaf59126cc0023d5d68486ba7cd5 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -368,6 +368,10 @@ class Expression : public AstNode {
   // True iff the expression is a valid target for an assignment.
   bool IsValidReferenceExpressionOrThis() const;
 
+  bool IsPatternOrLiteral() const {
+    return IsObjectLiteral() || IsArrayLiteral();
+  }
+
   // Expression type bounds
   Bounds bounds() const { return bounds_; }
   void set_bounds(Bounds bounds) { bounds_ = bounds; }
@@ -2356,6 +2360,11 @@ class Assignment final : public Expression {
   // This check relies on the definition order of token in token.h.
   bool is_compound() const { return op() > Token::ASSIGN; }
 
+  // Returns true if op is `=` and LHS is might be a pattern
+  bool IsDestructuring() const {
+    return op() == Token::ASSIGN && target()->IsPatternOrLiteral();
+  }
+
   static int num_ids() { return parent_num_ids() + 2; }
   BailoutId AssignmentId() const { return BailoutId(local_id(0)); }