[es7] implement exponentiation operator proposal

src/parsing/parser.h

Index: src/parsing/parser.h
diff --git a/src/parsing/parser.h b/src/parsing/parser.h
index 5f0176c76a7466f772292564056615cdc3e0baf9..7649dba6653102dbce97d54f0faa22fc44154654 100644
--- a/src/parsing/parser.h
+++ b/src/parsing/parser.h
@@ -640,6 +640,9 @@ class ParserTraits {
   // Rewrite all DestructuringAssignments in the current FunctionState.
   V8_INLINE void RewriteDestructuringAssignments();
 
+  V8_INLINE Expression* RewriteAssignExponentiation(Expression* left,
+                                                    Expression* right, int pos);
+
   V8_INLINE void QueueDestructuringAssignmentForRewriting(
       Expression* assignment);
 
@@ -1020,6 +1023,9 @@ class Parser : public ParserBase<ParserTraits> {
 
   V8_INLINE void RewriteDestructuringAssignments();
 
+  V8_INLINE Expression* RewriteAssignExponentiation(Expression* left,
+                                                    Expression* right, int pos);
+
   friend class NonPatternRewriter;
   V8_INLINE Expression* RewriteSpreads(ArrayLiteral* lit);