Parse harmony let declarations.

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index a87eecc3c55ebde14127a46393b2f587c9c99c41..c7e78067cfebce5161baaaf18ecc4520e33cfa92 100755
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -478,15 +478,21 @@ Handle<SharedFunctionInfo> Compiler::Compile(Handle<String> source,
     // that would be compiled lazily anyway, so we skip the preparse step
     // in that case too.
     ScriptDataImpl* pre_data = input_pre_data;
+    bool harmony_block_scoping = natives != NATIVES_CODE &&
+                                 FLAG_harmony_block_scoping;
     if (pre_data == NULL
         && source_length >= FLAG_min_preparse_length) {
       if (source->IsExternalTwoByteString()) {
         ExternalTwoByteStringUC16CharacterStream stream(
             Handle<ExternalTwoByteString>::cast(source), 0, source->length());
-        pre_data = ParserApi::PartialPreParse(&stream, extension);
+        pre_data = ParserApi::PartialPreParse(&stream,
+                                              extension,
+                                              harmony_block_scoping);
       } else {
         GenericStringUC16CharacterStream stream(source, 0, source->length());
-        pre_data = ParserApi::PartialPreParse(&stream, extension);
+        pre_data = ParserApi::PartialPreParse(&stream,
+                                              extension,
+                                              harmony_block_scoping);
       }
     }