Parse harmony let declarations.

src/preparser.h

Index: src/preparser.h
diff --git a/src/preparser.h b/src/preparser.h
index 3d72c97e2691862349b16416591314641ee4695a..bbf39119ef4734518c69c3efc723ea11b34b9f4a 100644
--- a/src/preparser.h
+++ b/src/preparser.h
@@ -377,12 +377,14 @@ class PreParser {
   // which is set to false if parsing failed; it is unchanged otherwise.
   // By making the 'exception handling' explicit, we are forced to check
   // for failure at the call sites.
+  Statement ParseSourceElement(bool* ok);
   SourceElements ParseSourceElements(int end_token, bool* ok);
   Statement ParseStatement(bool* ok);
   Statement ParseFunctionDeclaration(bool* ok);
   Statement ParseBlock(bool* ok);
-  Statement ParseVariableStatement(bool* ok);
-  Statement ParseVariableDeclarations(bool accept_IN, int* num_decl, bool* ok);
+  Statement ParseVariableStatement(bool accept_LET, bool* ok);
+  Statement ParseVariableDeclarations(bool accept_LET, bool accept_IN,
+                                      int* num_decl, bool* ok);
   Statement ParseExpressionOrLabelledStatement(bool* ok);
   Statement ParseIfStatement(bool* ok);
   Statement ParseContinueStatement(bool* ok);