don't update when nothing changed

Summary:
The QPL plugin is sending the current time on the device every second, this was causing state updates every second.

QPL: don't update the state, when we did not receive new traces.
Client: only dispatch the update event, when the new state is different from the current.

Reviewed By: passy

Differential Revision: D12956337

fbshipit-source-id: c006540097408ead8fb8c5aac3aaaa220c1a3951

src/Client.js

@@ -179,12 +179,14 @@ export default class Client extends EventEmitter {
             params.method,
             params.params,
           );
-          this.store.dispatch(
+          if (persistedState !== newPluginState) {
-            setPluginState({
+            this.store.dispatch(
-              pluginKey,
+              setPluginState({
-              state: newPluginState,
+                pluginKey,
-            }),
+                state: newPluginState,
-          );
+              }),
+            );
+          }
         } else {
           const apiCallbacks = this.broadcastCallbacks.get(params.api);
           if (!apiCallbacks) {