Revert of [debugger] flood function for stepping before calling it.

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 1ffaa5f95cab4d1e06d8f0b7b70b47c73c0068ec..8bdec1061b1f92af06c7938db61fdbe7d9b7c83c 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -1633,15 +1633,50 @@
 }
 
 
+// Check whether debugger is about to step into the callback that is passed
+// to a built-in function such as Array.forEach. This check is done before
+// %DebugPrepareStepInIfStepping and is not strictly necessary. However, if it
+// returns false, we can skip %DebugPrepareStepInIfStepping, useful in loops.
+RUNTIME_FUNCTION(Runtime_DebugCallbackSupportsStepping) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 1);
+  if (!DebugStepInIsActive(isolate->debug())) {
+    return isolate->heap()->false_value();
+  }
+  CONVERT_ARG_CHECKED(Object, object, 0);
+  RUNTIME_ASSERT(object->IsJSFunction() || object->IsJSGeneratorObject());
+  // We do not step into the callback if it's a builtin other than a bound,
+  // or not even a function.
+  JSFunction* fun;
+  if (object->IsJSFunction()) {
+    fun = JSFunction::cast(object);
+  } else {
+    fun = JSGeneratorObject::cast(object)->function();
+  }
+  return isolate->heap()->ToBoolean(fun->shared()->IsSubjectToDebugging() ||
+                                    fun->shared()->bound());
+}
+
+
+void FloodDebugSubjectWithOneShot(Debug* debug, Handle<JSFunction> function) {
+  if (function->shared()->IsSubjectToDebugging() ||
+      function->shared()->bound()) {
+    // When leaving the function, step out has been activated, but not performed
+    // if we do not leave the builtin.  To be able to step into the function
+    // again, we need to clear the step out at this point.
+    debug->ClearStepOut();
+    debug->FloodWithOneShotGeneric(function);
+  }
+}
+
+
 // Set one shot breakpoints for the callback function that is passed to a
 // built-in function such as Array.forEach to enable stepping into the callback,
 // if we are indeed stepping and the callback is subject to debugging.
 RUNTIME_FUNCTION(Runtime_DebugPrepareStepInIfStepping) {
   DCHECK(args.length() == 1);
   Debug* debug = isolate->debug();
-  if (debug->in_debug_scope() || !DebugStepInIsActive(debug)) {
-    return isolate->heap()->undefined_value();
-  }
+  if (!DebugStepInIsActive(debug)) return isolate->heap()->undefined_value();
 
   HandleScope scope(isolate);
   CONVERT_ARG_HANDLE_CHECKED(Object, object, 0);
@@ -1654,18 +1689,22 @@
         Handle<JSGeneratorObject>::cast(object)->function(), isolate);
   }
 
-  debug->ClearStepOut();
-  debug->FloodWithOneShotGeneric(fun);
+  FloodDebugSubjectWithOneShot(debug, fun);
   return isolate->heap()->undefined_value();
 }
 
 
 RUNTIME_FUNCTION(Runtime_DebugPushPromise) {
-  DCHECK(args.length() == 2);
+  DCHECK(args.length() == 3);
   HandleScope scope(isolate);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, promise, 0);
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 1);
+  CONVERT_ARG_HANDLE_CHECKED(Object, handler, 2);
   isolate->PushPromise(promise, function);
+  Debug* debug = isolate->debug();
+  if (handler->IsJSFunction() && DebugStepInIsActive(debug)) {
+    FloodDebugSubjectWithOneShot(debug, Handle<JSFunction>::cast(handler));
+  }
   return isolate->heap()->undefined_value();
 }