Allow stepping into Object.observe handlers.

src/runtime/runtime-observe.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/arguments.h"
+#include "src/debug.h"
 #include "src/runtime/runtime-utils.h"
 
 namespace v8 {
 namespace internal {
 
 RUNTIME_FUNCTION(Runtime_IsObserved) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 1);
 
   if (!args[0]->IsJSReceiver()) return isolate->heap()->false_value();
@@ skipping 38 matching lines @@
   HandleScope scope(isolate);
   DCHECK(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, callback, 0);
   CONVERT_ARG_HANDLE_CHECKED(Object, argument, 1);
   v8::TryCatch catcher;
   // We should send a message on uncaught exception thrown during
   // Object.observe delivery while not interrupting further delivery, thus
   // we make a call inside a verbose TryCatch.
   catcher.SetVerbose(true);
   Handle<Object> argv[] = {argument};
+
+  // Allow stepping into the observer callback.
+  Debug* debug = isolate->debug();
+  if (debug->is_active() && debug->IsStepping() &&
+      debug->last_step_action() == StepIn) {
+    // Previous StepIn may have activated a StepOut if it was at the frame exit.
+    // In this case to be able to step into the callback again, we need to clear
+    // the step out first.
+    debug->ClearStepOut();
+    debug->FloodWithOneShot(callback);
+  }
+
   USE(Execution::Call(isolate, callback, isolate->factory()->undefined_value(),
                       arraysize(argv), argv));
   if (isolate->has_pending_exception()) {
     isolate->ReportPendingMessages();
     isolate->clear_pending_exception();
     isolate->set_external_caught_exception(false);
   }
   return isolate->heap()->undefined_value();
 }
 
@@ skipping 62 matching lines @@
 RUNTIME_FUNCTION(Runtime_GetObjectContextNotifierPerformChange) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, object_info, 0);
 
   Handle<Context> context(object_info->GetCreationContext(), isolate);
   return context->native_object_notifier_perform_change();
 }
 }
 }  // namespace v8::internal