libbinder: Document future direction of getService.

I've had a CL a long time which did this here:
https://android-review.googlesource.com/c/platform/frameworks/native/+/1225405/

However, I am not sure how to get confidence in it, and it changes
threading structure, scheduling structure, etc... So I don't think it's
quite the right time to merge it yet.

Bug: n/a
Test: n/a
Change-Id: I83549b920a470387484245587a4714b69765f03f
diff --git a/libs/binder/IServiceManager.cpp b/libs/binder/IServiceManager.cpp
index 9888b59..dab7ad5 100644
--- a/libs/binder/IServiceManager.cpp
+++ b/libs/binder/IServiceManager.cpp
@@ -205,6 +205,10 @@
  : mTheRealServiceManager(impl)
 {}
 
+// This implementation could be simplified and made more efficient by delegating
+// to waitForService. However, this changes the threading structure in some
+// cases and could potentially break prebuilts. Once we have higher logistical
+// complexity, this could be attempted.
 sp<IBinder> ServiceManagerShim::getService(const String16& name) const
 {
     static bool gSystemBootCompleted = false;