Fix preparsing from a source string that is not external....

src/scanner.cc

Index: src/scanner.cc
===================================================================
--- src/scanner.cc	(revision 5044)
+++ src/scanner.cc	(working copy)
@@ -341,8 +341,7 @@
 
 void Scanner::Initialize(Handle<String> source,
                          ParserLanguage language) {
-  safe_string_input_buffer_.Reset(source.location());
-  Init(source, &safe_string_input_buffer_, 0, source->length(), language);
+  Init(source, NULL, 0, source->length(), language);
 }
 
 
@@ -357,9 +356,7 @@
                          int start_position,
                          int end_position,
                          ParserLanguage language) {
-  safe_string_input_buffer_.Reset(source.location());
-  Init(source, &safe_string_input_buffer_,
-       start_position, end_position, language);
+  Init(source, NULL, start_position, end_position, language);
 }
 
 
@@ -368,6 +365,10 @@
                    int start_position,
                    int end_position,
                    ParserLanguage language) {
+  // Either initialize the scanner from a character stream or from a
+  // string.
+  ASSERT(source.is_null() || stream == NULL);
+
   // Initialize the source buffer.
   if (!source.is_null() && StringShape(*source).IsExternalTwoByte()) {
     two_byte_string_buffer_.Initialize(
@@ -382,6 +383,10 @@
         end_position);
     source_ = &ascii_string_buffer_;
   } else {
+    if (!source.is_null()) {
+      safe_string_input_buffer_.Reset(source.location());
+      stream = &safe_string_input_buffer_;
+    }
     char_stream_buffer_.Initialize(source,
                                    stream,
                                    start_position,