Convert ReadMessage...() to use the new user pointer handling (see r285350).

mojo/system/core_test_base.cc

Index: mojo/system/core_test_base.cc
diff --git a/mojo/system/core_test_base.cc b/mojo/system/core_test_base.cc
index bde8c697e2cca65f579da89f7866e2e452e16f8d..2fbcc989806ce849acc7eb73fd06b241b130ef57 100644
--- a/mojo/system/core_test_base.cc
+++ b/mojo/system/core_test_base.cc
@@ -66,17 +66,14 @@ class MockDispatcher : public Dispatcher {
   }
 
   virtual MojoResult ReadMessageImplNoLock(
-      void* bytes,
-      uint32_t* num_bytes,
+      UserPointer<void> bytes,
+      UserPointer<uint32_t> num_bytes,
       DispatcherVector* dispatchers,
       uint32_t* num_dispatchers,
       MojoReadMessageFlags /*flags*/) OVERRIDE {
     info_->IncrementReadMessageCallCount();
     lock().AssertAcquired();
 
-    if (num_bytes && !VerifyUserPointerWithSize<1>(bytes, *num_bytes))
-      return MOJO_RESULT_INVALID_ARGUMENT;
-
     if (num_dispatchers) {
       *num_dispatchers = 1;
       if (dispatchers) {