Introduce phantom weak handles in the API and use them internally for debug info

src/compiler.cc

Index: src/compiler.cc
diff --git a/src/compiler.cc b/src/compiler.cc
index b7e0c98f5e2ac2dbf97f756aca85f815375769c0..ba5f3fd56ea511d39162be59ff77f22f85cc9c22 100644
--- a/src/compiler.cc
+++ b/src/compiler.cc
@@ -1308,7 +1308,7 @@ Handle<SharedFunctionInfo> Compiler::BuildFunctionInfo(
 
   if (outer_info->is_toplevel() && outer_info->will_serialize()) {
     // Make sure that if the toplevel code (possibly to be serialized),
-    // the inner unction must be allowed to be compiled lazily.
+    // the inner function must be allowed to be compiled lazily.
     DCHECK(allow_lazy);
   }