Allow uncaught exception messaging in Object.observe callbacks.

test/cctest/test-debug.cc

Index: test/cctest/test-debug.cc
diff --git a/test/cctest/test-debug.cc b/test/cctest/test-debug.cc
index 575f938594cbe6f9011d89c11838af29cefc9c9d..5d38a16aee6ef566ecce9664c3f37018a60869bc 100644
--- a/test/cctest/test-debug.cc
+++ b/test/cctest/test-debug.cc
@@ -7594,3 +7594,29 @@ TEST(DebugPromiseRejectedByCallback) {
   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);
+}