core: Unify initial channel startup queuing delay reason to 'client channel: waiting for picker' per gRFC spec

Author: AgraVator

core/src/main/java/io/grpc/internal/DelayedClientTransport.java

@@ -382,7 +382,7 @@ private static String determineQueuingDelayType(@Nullable PickResult pickResult)
 
   private static String determineQueuingDelayReason(@Nullable PickResult pickResult) {
     if (pickResult == null) {
-      return "client channel: created LB policy.";
+      return "client channel: waiting for picker";
     }
     if (pickResult.getSubchannel() != null) {
       return "subchannel returned by LB picker has no connected subchannel";

core/src/test/java/io/grpc/internal/DelayedClientTransportTest.java

@@ -879,7 +879,7 @@ public void streamDelayMetrics_channelFallback_clientChannelInit() {
     delayedTransport.newStream(method, headers, callOptions, customTracers);
 
     verify(mockTracer).recordAttemptDelayStart(
-        "connecting", "client channel: created LB policy.");
+        "connecting", "client channel: waiting for picker");
   }
 
   @Test