Disable false positives for StoreGaugesAsMemberVariables lint rule

Problem

We have a new scalafix lint rule, StoreGaugesAsMemberVariables, that
flags cases where Gauges are not stored in member variables.

However, because it is a syntactic rule, it sometimes flags some false
positives.

Solution

Disable the rule where appropriate.

JIRA Issues: CSL-6746

TBR=true

Differential Revision: https://phabricator.twitter.biz/D214652

finagle-http2/src/main/scala/com/twitter/finagle/http2/ServerCodec.scala

@@ -33,12 +33,14 @@ private[http2] object ServerCodec {
     http2MultiplexCodec: Http2MultiplexCodec,
     channel: Channel
   ): Unit = {
+    // scalafix:off StoreGaugesAsMemberVariables
     val streams = statsReceiver.addGauge("streams") {
       // Note that this isn't thread-safe because the session state is intended to be
       // single-threaded and used only from within the channel, but addressing that
       // would be very challenging.
       http2MultiplexCodec.connection.numActiveStreams
     }
+    // scalafix:on StoreGaugesAsMemberVariables
 
     // We're attaching a gauge to the channel's attributes to make sure it stays referenced
     // as long as channel is alive.

finagle-serversets/src/main/scala/com/twitter/finagle/serverset2/HealthStabilizer.scala

@@ -54,6 +54,7 @@ private[serverset2] object HealthStabilizer {
 
       val currentStatus = new AtomicReference[Status]()
       val gaugeListener = stateChanges.dedup.register(Witness { currentStatus })
+      // scalafix:off StoreGaugesAsMemberVariables
       val gauge = statsReceiver.addGauge("zkHealth") {
         currentStatus.get() match {
           case Unknown => 0
@@ -62,6 +63,7 @@ private[serverset2] object HealthStabilizer {
           case Probation(_) => 3
         }
       }
+      // scalafix:on StoreGaugesAsMemberVariables
 
       val notify = stateChanges
         .collect {

finagle-stats/src/test/scala/com/twitter/finagle/stats/MetricsStatsReceiverTest.scala

@@ -10,7 +10,7 @@ class MetricsStatsReceiverTest extends FunSuite {
 
   private[this] def readGaugeInRoot(name: String) = readGauge(rootReceiver, name)
   private[this] def readCounterInRoot(name: String) = rootReceiver.registry.counters.get(name)
-
+  // scalafix:off StoreGaugesAsMemberVariables
   test("MetricsStatsReceiver should store and read gauge into the root StatsReceiver") {
     val x = 1.5f
     // gauges are weakly referenced by the registry so we need to keep a strong reference
@@ -134,4 +134,5 @@ class MetricsStatsReceiverTest extends FunSuite {
     assert(metrics1.histograms.containsKey("baz"))
     assert(metrics2.histograms.containsKey("baz"))
   }
+  // scalafix:on StoreGaugesAsMemberVariables
 }