fix(sync-worker): Never paginate faster than 1 page per 1.5sec

This should prevent us from flooding the app with contacts (/contacts responds very quickly). Fixes T3475

internal_packages/worker-sync/lib/nylas-sync-worker.coffee

@@ -132,6 +132,7 @@ class NylasSyncWorker
         @_resumeTimer.start()
 
   fetchCollectionPage: (model, params = {}) ->
+    requestStartTime = Date.now()
     requestOptions =
       error: (err) =>
         return if @_terminated
@@ -143,7 +144,8 @@ class NylasSyncWorker
         lastReceivedIndex = params.offset + json.length
         if json.length is params.limit
           nextParams = _.extend({}, params, {offset: lastReceivedIndex})
-          @fetchCollectionPage(model, nextParams)
+          nextDelay = Math.max(0, 1500 - (Date.now() - requestStartTime))
+          setTimeout(( => @fetchCollectionPage(model, nextParams)), nextDelay)
           @updateTransferState(model, {fetched: lastReceivedIndex})
         else
           @updateTransferState(model, {fetched: lastReceivedIndex, busy: false, complete: true})

internal_packages/worker-sync/spec/nylas-sync-worker-spec.coffee

@@ -170,6 +170,7 @@ describe "NylasSyncWorker", ->
         models = []
         models.push(new Thread) for i in [0..(pageSize-1)]
         @request.requestOptions.success(models)
+        advanceClock(2000)
         expect(@apiRequests.length).toBe(1)
         expect(@apiRequests[0].params).toEqual
           limit: pageSize,