core: Apply ManagedChannelImpl's updateBalancingState() immediately

ffcc360 adjusted updateBalancingState() to require being run within
the sync context. However, it still queued the work into the sync
context, which was unnecessary. This re-entering the sync context
unnecessarily delays the new state from being used.

Author: ejona86

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

@@ -1388,24 +1388,18 @@ public void updateBalancingState(
       syncContext.throwIfNotInThisSynchronizationContext();
       checkNotNull(newState, "newState");
       checkNotNull(newPicker, "newPicker");
-      final class UpdateBalancingState implements Runnable {
-        @Override
-        public void run() {
-          if (LbHelperImpl.this != lbHelper || panicMode) {
-            return;
-          }
-          updateSubchannelPicker(newPicker);
-          // It's not appropriate to report SHUTDOWN state from lb.
-          // Ignore the case of newState == SHUTDOWN for now.
-          if (newState != SHUTDOWN) {
-            channelLogger.log(
-                ChannelLogLevel.INFO, "Entering {0} state with picker: {1}", newState, newPicker);
-            channelStateManager.gotoState(newState);
-          }
-        }
-      }
 
-      syncContext.execute(new UpdateBalancingState());
+      if (LbHelperImpl.this != lbHelper || panicMode) {
+        return;
+      }
+      updateSubchannelPicker(newPicker);
+      // It's not appropriate to report SHUTDOWN state from lb.
+      // Ignore the case of newState == SHUTDOWN for now.
+      if (newState != SHUTDOWN) {
+        channelLogger.log(
+            ChannelLogLevel.INFO, "Entering {0} state with picker: {1}", newState, newPicker);
+        channelStateManager.gotoState(newState);
+      }
     }
 
     @Override