Revert "Revert "Synchronizing loader preload to avoid launcher getting stuck in loading state,""

This reverts commit 73aa3025c0.

Reason for revert: Post-drop revert

Change-Id: Ife752d26e07d9c064c938ff8d33d40457b54217a

src/com/android/launcher3/LauncherModel.java

@@ -493,6 +493,15 @@ public class LauncherModel extends BroadcastReceiver
         }
     }
 
+    public void startLoaderForResultsIfNotLoaded(LoaderResults results) {
+        synchronized (mLock) {
+            if (!isModelLoaded()) {
+                Log.d(TAG, "Workspace not loaded, loading now");
+                startLoaderForResults(results);
+            }
+        }
+    }
+
     /**
      * Loads the workspace screen ids in an ordered list.
      */

src/com/android/launcher3/model/ModelPreload.java

@@ -49,11 +49,8 @@ public class ModelPreload implements ModelUpdateTask {
 
     @Override
     public final void run() {
-        if (!mModel.isModelLoaded()) {
-            Log.d(TAG, "Workspace not loaded, loading now");
-            mModel.startLoaderForResults(
-                    new LoaderResults(mApp, mBgDataModel, mAllAppsList, 0, null));
-        }
+        mModel.startLoaderForResultsIfNotLoaded(
+                new LoaderResults(mApp, mBgDataModel, mAllAppsList, 0, null));
         Log.d(TAG, "Preload completed : " + mModel.isModelLoaded());
         onComplete(mModel.isModelLoaded());
     }