[inspector] fixed console.count with empty stack

BUG=chromium:644629
R=dgozman@chromium.org

Review-Url: https://codereview.chromium.org/2372093002
Cr-Commit-Position: refs/heads/master@{#39786}

src/inspector/v8-console.cc

@@ -344,9 +344,10 @@ void V8Console::countCallback(const v8::FunctionCallbackInfo<v8::Value>& info) {
   if (title.isEmpty()) {
     std::unique_ptr<V8StackTraceImpl> stackTrace =
         V8StackTraceImpl::capture(nullptr, 0, 1);
-    if (stackTrace)
+    if (stackTrace && !stackTrace->isEmpty()) {
       identifier = toString16(stackTrace->topSourceURL()) + ":" +
                    String16::fromInteger(stackTrace->topLineNumber());
+    }
   } else {
     identifier = title + "@";
   }