Give that code some comments; code loves comments

Author: ejona86

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

@@ -89,11 +89,16 @@ final void setStream(ClientStream stream) {
           passThrough = true;
           break;
         }
+        // Since there were pendingCalls, we need to process them. To maintain ordering we can't set
+        // passThrough=true until we run all pendingCalls, but new Runnables may be added after we
+        // drop the lock. So we will have to re-check pendingCalls.
         List<Runnable> tmp = toRun;
         toRun = pendingCalls;
         pendingCalls = tmp;
       }
       for (Runnable runnable : toRun) {
+        // Must not call transport while lock is held to prevent deadlocks.
+        // TODO(ejona): exception handling
         runnable.run();
       }
       toRun.clear();