[debugger] Hide scopes that originate from desugaring.

src/ast/scopes.cc

Index: src/ast/scopes.cc
diff --git a/src/ast/scopes.cc b/src/ast/scopes.cc
index 5d4b80987607b531c423a35c04cdec582a870371..c82ec698d210889b666913b42c7e3c6a619797cc 100644
--- a/src/ast/scopes.cc
+++ b/src/ast/scopes.cc
@@ -193,6 +193,7 @@ void Scope::SetDefaults(ScopeType scope_type, Scope* outer_scope,
   scope_info_ = scope_info;
   start_position_ = RelocInfo::kNoPosition;
   end_position_ = RelocInfo::kNoPosition;
+  is_hidden_ = false;
   if (!scope_info.is_null()) {
     scope_calls_eval_ = scope_info->CallsEval();
     language_mode_ = scope_info->language_mode();
@@ -287,6 +288,7 @@ bool Scope::Analyze(ParseInfo* info) {
                                : FLAG_print_scopes) {
     scope->Print();
   }
+  scope->CheckScopePositions();
 #endif
 
   info->set_scope(scope);
@@ -1007,6 +1009,16 @@ void Scope::Print(int n) {
 
   Indent(n0, "}\n");
 }
+
+void Scope::CheckScopePositions() {
+  // A scope is allowed to have invalid positions if it is hidden and has no
+  // inner scopes
+  if (!is_hidden() && inner_scopes_.length() == 0) {
+    CHECK_NE(RelocInfo::kNoPosition, start_position());
+    CHECK_NE(RelocInfo::kNoPosition, end_position());
+  }
+  for (Scope* scope : inner_scopes_) scope->CheckScopePositions();
+}
 #endif  // DEBUG