Optimized scanner to avoid virtual calls for every character read.

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index 59a684c69f63c4d68d44f2a8dc40ae08323c9063..a52f3c2ebe5a52f8c4a5732238deab88be9faead 100755
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -461,7 +461,14 @@ Handle<SharedFunctionInfo> Compiler::Compile(Handle<String> source,
     ScriptDataImpl* pre_data = input_pre_data;
     if (pre_data == NULL
         && source_length >= FLAG_min_preparse_length) {
-      pre_data = ParserApi::PartialPreParse(source, NULL, extension);
+      if (source->IsExternalTwoByteString()) {
+        ExternalTwoByteStringUC16CharacterStream stream(
+            Handle<ExternalTwoByteString>::cast(source), 0, source->length());
+        pre_data = ParserApi::PartialPreParse(&stream, extension);
+      } else {
+        GenericStringUC16CharacterStream stream(source, 0, source->length());
+        pre_data = ParserApi::PartialPreParse(&stream, extension);
+      }
     }
 
     // Create a script object describing the script to be compiled.