Implement experimental exponentiation operator

src/scanner.cc

Index: src/scanner.cc
diff --git a/src/scanner.cc b/src/scanner.cc
index de1b8e8b7202d211b297e8ca5737fb8f411299ed..267ae86204e3b7adfd79dc4f7694fc64bab47600 100644
--- a/src/scanner.cc
+++ b/src/scanner.cc
@@ -40,7 +40,8 @@ Scanner::Scanner(UnicodeCache* unicode_cache)
       harmony_numeric_literals_(false),
       harmony_classes_(false),
       harmony_templates_(false),
-      harmony_unicode_(false) {}
+      harmony_unicode_(false),
+      harmony_exponentiation_(false) {}
 
 
 void Scanner::Initialize(Utf16CharacterStream* source) {
@@ -533,8 +534,19 @@ void Scanner::Scan() {
         break;
 
       case '*':
-        // * *=
-        token = Select('=', Token::ASSIGN_MUL, Token::MUL);
+        // * *= ** **=
+        Advance();
+        if (c0_ == '*') {
+          if (HarmonyExponentiation()) {
+            token = Select('=', Token::ASSIGN_EXP, Token::EXP);
+          } else {
+            token = Token::ILLEGAL;
+          }
+        } else if (c0_ == '=') {
+          token = Select(Token::ASSIGN_MUL);
+        } else {
+          token = Token::MUL;
+        }
         break;
 
       case '%':