title: Adding Toolbar to ConstraintLayout
body: <p>When I try to add <code>ToolBar</code> to <code>ConstraintLayout</code> nothing is shown in the component tree and I get the following error :</p>
  
  <pre><code>java.lang.NoClassDefFoundError: android/support/constraint/R$styleable
      at android.support.constraint.ConstraintLayout$LayoutParams.&lt;init&gt;(ConstraintLayout.java:644)
      at android.support.constraint.ConstraintLayout.generateLayoutParams(ConstraintLayout.java:572)
      at android.support.constraint.ConstraintLayout.generateLayoutParams(ConstraintLayout.java:47)
      at android.view.LayoutInflater.rInflate_Original(LayoutInflater.java:860)
      at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:70)
      at android.view.LayoutInflater.rInflate(LayoutInflater.java:834)
      at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:821)
      at android.view.LayoutInflater.inflate(LayoutInflater.java:518)
      at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
      at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:317)
      at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:429)
      at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:389)
      at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:548)
      at com.android.tools.idea.rendering.RenderTask$2.compute(RenderTask.java:533)
      at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:966)
      at com.android.tools.idea.rendering.RenderTask.createRenderSession(RenderTask.java:533)
      at com.android.tools.idea.rendering.RenderTask.lambda$inflate$58(RenderTask.java:659)
      at com.android.tools.idea.rendering.RenderService.runRenderAction(RenderService.java:380)
      at com.android.tools.idea.rendering.RenderTask.inflate(RenderTask.java:659)
      at com.android.tools.idea.uibuilder.model.NlModel.inflate(NlModel.java:327)
      at com.android.tools.idea.uibuilder.model.NlModel.render(NlModel.java:384)
      at com.android.tools.idea.uibuilder.surface.DesignSurface$3.modelChanged(DesignSurface.java:875)
      at com.android.tools.idea.uibuilder.model.NlModel.lambda$notifyListenersModelUpdateComplete$71(NlModel.java:460)
      at java.lang.Iterable.forEach(Iterable.java:75)
      at com.android.tools.idea.uibuilder.model.NlModel.notifyListenersModelUpdateComplete(NlModel.java:460)
      at com.android.tools.idea.uibuilder.model.NlModel.updateModel(NlModel.java:374)
      at com.android.tools.idea.uibuilder.model.NlModel$1.run(NlModel.java:237)
      at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:333)
      at com.intellij.util.ui.update.MergingUpdateQueue.execute(MergingUpdateQueue.java:323)
      at com.intellij.util.ui.update.MergingUpdateQueue$3.run(MergingUpdateQueue.java:267)
      at com.intellij.util.ui.update.MergingUpdateQueue.flush(MergingUpdateQueue.java:282)
      at com.intellij.util.ui.update.MergingUpdateQueue.run(MergingUpdateQueue.java:234)
      at com.intellij.util.concurrency.QueueProcessor.runSafely(QueueProcessor.java:238)
      at com.intellij.util.Alarm$Request$1.run(Alarm.java:378)
      at com.intellij.util.Alarm$Request.run(Alarm.java:389)
      at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
      at java.util.concurrent.FutureTask.run(FutureTask.java:266)
      at com.intellij.util.concurrency.SchedulingWrapper$MyScheduledFutureTask.run(SchedulingWrapper.java:227)
      at com.intellij.util.concurrency.BoundedTaskExecutor$2.run(BoundedTaskExecutor.java:187)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
      at java.lang.Thread.run(Thread.java:745)
  </code></pre>
  
  <p>Any hint will be appreciated</p>