Add plugin support

- Add libs/plugin_core.jar
- Include plugin_core in Launcher3 build (it is already present other
  builds as part of the updated shared lib)
- Add PluginEnablerImpl that uses SharedPrefs to enable/disable plugin
  components
- Add src_plugins, where plugin interfaces will live. It has a build
  rule to create a jar that plugin projects will depend on.
- Copy PluginPreferencesFragment from sysui but using our implementation
  for PluginEnabler

Bug: 115877296
Change-Id: I3db54677eaceb10f92018c0f9d18920ad9ffac39

quickstep/src/com/android/launcher3/uioverrides/plugins/PluginManagerWrapper.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the
+ * License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the specific language governing
+ * permissions and limitations under the License.
+ */
+
+package com.android.launcher3.uioverrides.plugins;
+
+import android.content.Context;
+
+import com.android.launcher3.util.MainThreadInitializedObject;
+import com.android.systemui.plugins.Plugin;
+import com.android.systemui.plugins.PluginListener;
+import com.android.systemui.shared.plugins.PluginEnabler;
+import com.android.systemui.shared.plugins.PluginInitializer;
+import com.android.systemui.shared.plugins.PluginManager;
+import com.android.systemui.shared.plugins.PluginManagerImpl;
+
+public class PluginManagerWrapper {
+
+    public static final MainThreadInitializedObject<PluginManagerWrapper> INSTANCE =
+            new MainThreadInitializedObject<>(PluginManagerWrapper::new);
+
+    private final PluginManager mPluginManager;
+    private final PluginEnabler mPluginEnabler;
+
+    private PluginManagerWrapper(Context c) {
+        PluginInitializer pluginInitializer  = new PluginInitializerImpl();
+        mPluginManager = new PluginManagerImpl(c, pluginInitializer);
+        mPluginEnabler = pluginInitializer.getPluginEnabler(c);
+    }
+
+    PluginEnabler getPluginEnabler() {
+        return mPluginEnabler;
+    }
+
+    public void addPluginListener(PluginListener<? extends Plugin> listener, Class<?> pluginClass) {
+        mPluginManager.addPluginListener(listener, pluginClass);
+    }
+
+    public void removePluginListener(PluginListener<? extends Plugin> listener) {
+        mPluginManager.removePluginListener(listener);
+    }
+}