Setup sdk for background plugin

Summary:
This diff sets up flipper for running plugins in background. This diff does the following

- Adds a function named `runInBackground` to the interface `FlipperPlugin` to make the plugins opt in to be run in background, default is false
- Changes the javascript side of the flipper to store the messages received by the plugins in background
- Process the stored messages when the plugin in background becomes active
- Currently I have just turned on network plugin to be in background mode.

- Remove the buffering from the network plugin, as it will run in background
- Write a batching layer to batch the messages and send to flipper.

Note: I haven't tested the wilde app yet, but the sample app works. I will remove the "[WIP]" from the title once I have tested it in wilde

Reviewed By: danielbuechele

Differential Revision: D10301403

fbshipit-source-id: 034eebf659a545d6b480a4ac1b73b0aa4b2f9797

src/PluginContainer.js

@@ -119,6 +119,9 @@ class PluginContainer extends Component<Props, State> {
     if (ref && target) {
       activateMenuItems(ref);
       ref._init();
+      if (target instanceof Client) {
+        target.readBufferedMessages(ref.constructor.id);
+      }
       this.props.logger.trackTimeSince(`activePlugin-${ref.constructor.id}`);
       this.plugin = ref;
     }
@@ -136,7 +139,13 @@ class PluginContainer extends Component<Props, State> {
       key: pluginKey,
       logger: this.props.logger,
       persistedState: pluginStates[pluginKey] || {},
-      setPersistedState: state => setPluginState({pluginKey, state}),
+      setPersistedState: state => {
+        // We are using setTimout here to wait for previous state updated to
+        // finish before triggering a new state update. Otherwise this can
+        // cause race conditions, with multiple state updates happening at the
+        // same time.
+        setTimeout(() => setPluginState({pluginKey, state}), 0);
+      },
       target,
       deepLinkPayload: this.props.deepLinkPayload,
       ref: this.refChanged,