Allow uncaught exception messaging in Object.observe callbacks.

test/cctest/test-debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 7576 matching lines @@
   env->Global()->Set(v8_str("fun"), fun->GetFunction());
 
   CompileRun("var p = new Promise(function(res, rej) { fun(); res(); });");
   CompileRun(
       "var r;"
       "p.chain(function() { r = 'resolved'; },"
       "        function(e) { r = 'rejected' + e; });");
   CHECK(CompileRun("r")->Equals(v8_str("rejectedrejection")));
   CHECK_EQ(1, exception_event_counter);
 }
+
+
+TEST(DebugBreakOnExceptionInObserveCallback) {
+  DebugLocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope scope(isolate);
+  v8::Debug::SetDebugEventListener(&DebugEventCountException);
+  // Break on uncaught exception
+  ChangeBreakOnException(false, true);
+  exception_event_counter = 0;
+
+  v8::Handle<v8::FunctionTemplate> fun =
+      v8::FunctionTemplate::New(isolate, ThrowCallback);
+  env->Global()->Set(v8_str("fun"), fun->GetFunction());
+
+  CompileRun(
+      "var obj = {};"
+      "var callbackRan = false;"
+      "Object.observe(obj, function() {"
+      "   callbackRan = true;"
+      "   throw Error('foo');"
+      "});"
+      "obj.prop = 1");
+  CHECK(CompileRun("callbackRan")->BooleanValue());
+  CHECK_EQ(1, exception_event_counter);
+}