Fix warnings on Win64.

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index c8b79a4359f0ff986447ab88df507cb6b530a77e..ec6a23bc8b9b333b151ae942fbaf9ee6f0439f19 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -102,7 +102,9 @@ class BreakLocationIterator {
   void ClearAllDebugBreak();
 
 
-  inline int code_position() { return pc() - debug_info_->code()->entry(); }
+  inline int code_position() {
+    return static_cast<int>(pc() - debug_info_->code()->entry());
+  }
   inline int break_point() { return break_point_; }
   inline int position() { return position_; }
   inline int statement_position() { return statement_position_; }