[memprof] Add an assert to InstrProfWriter::addMemProfData

This patch adds a quick validity check to
InstrProfWriter::addMemProfData.  Specifically, we check to see if we
have all (or none) of the MemProf profile components (frames, call
stacks, records).

The credit goes to Teresa Johnson for suggesting this assert.

llvm/lib/ProfileData/InstrProfWriter.cpp

@@ -351,9 +351,14 @@ bool InstrProfWriter::addMemProfCallStack(
 
 bool InstrProfWriter::addMemProfData(memprof::IndexedMemProfData Incoming,
                                      function_ref<void(Error)> Warn) {
-  // TODO: Once we remove support for MemProf format Version V1, assert that
-  // the three components (frames, call stacks, and records) are either all
-  // empty or populated.
+  // Return immediately if everything is empty.
+  if (Incoming.Frames.empty() && Incoming.CallStacks.empty() &&
+      Incoming.Records.empty())
+    return true;
+
+  // Otherwise, every component must be non-empty.
+  assert(!Incoming.Frames.empty() && !Incoming.CallStacks.empty() &&
+         !Incoming.Records.empty());
 
   if (MemProfData.Frames.empty())
     MemProfData.Frames = std::move(Incoming.Frames);