[debug] implement intuitive semantics for stepping over await call.

src/assembler.h

Index: src/assembler.h
diff --git a/src/assembler.h b/src/assembler.h
index 353abdbbc163000fb8175d523c6d5950a7d59d76..d92980c6b9c8463225cdcae6b538c839eb217d39 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -1067,6 +1067,9 @@ class ExternalReference BASE_EMBEDDED {
   // Used to check if single stepping is enabled in generated code.
   static ExternalReference debug_step_in_enabled_address(Isolate* isolate);
 
+  // Used to check for suspended generator, used for stepping across await call.
+  static ExternalReference debug_suspended_generator_address(Isolate* isolate);
+
 #ifndef V8_INTERPRETED_REGEXP
   // C functions called from RegExp generated code.