b=788399 always use async drawing for OOP windowless plugins r=bsmedberg

dom/plugins/base/nsNPAPIPluginInstance.cpp

@@ -171,12 +171,7 @@ nsNPAPIPluginInstance::nsNPAPIPluginInstance()
     mPlugin(nullptr),
     mMIMEType(nullptr),
     mOwner(nullptr),
-    mCurrentPluginEvent(nullptr),
-#if defined(MOZ_X11) || defined(XP_WIN) || defined(XP_MACOSX)
-    mUsePluginLayersPref(true)
-#else
-    mUsePluginLayersPref(false)
-#endif
+    mCurrentPluginEvent(nullptr)
 #ifdef MOZ_WIDGET_ANDROID
   , mOnScreen(true)
 #endif
@@ -184,9 +179,6 @@ nsNPAPIPluginInstance::nsNPAPIPluginInstance()
   mNPP.pdata = NULL;
   mNPP.ndata = this;
 
-  mUsePluginLayersPref =
-    Preferences::GetBool("plugins.use_layers", mUsePluginLayersPref);
-
   PLUGIN_LOG(PLUGIN_LOG_BASIC, ("nsNPAPIPluginInstance ctor: this=%p\n",this));
 }
 
@@ -1212,13 +1204,8 @@ nsNPAPIPluginInstance::NotifyPainted(void)
 }
 
 nsresult
-nsNPAPIPluginInstance::UseAsyncPainting(bool* aIsAsync)
+nsNPAPIPluginInstance::GetIsOOP(bool* aIsAsync)
 {
-  if (!mUsePluginLayersPref) {
-    *aIsAsync = mUsePluginLayersPref;
-    return NS_OK;
-  }
-
   AutoPluginLibraryCall library(this);
   if (!library)
     return NS_ERROR_FAILURE;