[debugger] fix switch block source positions.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index 5fade0b3b7dd1ca2ee69995ea0c56d5b5a8ad278..389ec0020204c2ee6b2c45f86df51ce11b4d420b 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -1665,6 +1665,10 @@ Statement* Parser::RewriteSwitchStatement(Expression* tag,
   Block* cases_block = factory()->NewBlock(NULL, 1, false, kNoSourcePosition);
   cases_block->statements()->Add(switch_statement, zone());
   cases_block->set_scope(scope);
+  DCHECK_IMPLIES(scope != nullptr,
+                 switch_statement->position() >= scope->start_position());
+  DCHECK_IMPLIES(scope != nullptr,
+                 switch_statement->position() < scope->end_position());
   switch_block->statements()->Add(cases_block, zone());
   return switch_block;
 }