Remove "is function lazy" logic from Preparser + tiny error reporting refactoring.

src/parsing/preparse-data.h

Index: src/parsing/preparse-data.h
diff --git a/src/parsing/preparse-data.h b/src/parsing/preparse-data.h
index ddc4d03321aba8f1a28559087d2cdcaca1967585..e8e909f855125e874d3e049be75fcb7d742b18fb 100644
--- a/src/parsing/preparse-data.h
+++ b/src/parsing/preparse-data.h
@@ -81,6 +81,8 @@ class SingletonLogger : public ParserRecorder {
                            LanguageMode language_mode, bool uses_super_property,
                            bool calls_eval) {
     DCHECK(!has_error_);
+    // Check that we only log at most one function.
+    DCHECK(start_ == -1 && end_ == -1);
     start_ = start;
     end_ = end;
     literals_ = literals;