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

src/runtime/runtime-debug.cc

Index: src/runtime/runtime-debug.cc
diff --git a/src/runtime/runtime-debug.cc b/src/runtime/runtime-debug.cc
index e90e9d5fc463efbb3fc45cb31cb02ee307355a8d..601dbe3ce0ba4b81cb0771d394ffff7d61ae301c 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -1698,6 +1698,13 @@ RUNTIME_FUNCTION(Runtime_DebugPrepareStepInIfStepping) {
   return isolate->heap()->undefined_value();
 }
 
+// Set one shot breakpoints for the suspended generator object.
+RUNTIME_FUNCTION(Runtime_DebugPrepareStepInSuspendedGenerator) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(0, args.length());
+  isolate->debug()->PrepareStepInSuspendedGenerator();
+  return isolate->heap()->undefined_value();
+}
 
 RUNTIME_FUNCTION(Runtime_DebugPushPromise) {
   DCHECK(args.length() == 2);