message: Add some logging to indicate misses in the XLA compilation cache.
diff: @@ -295,6 +295,8 @@ Status XlaCompilationCache::Compile(
  // cache eviction.
  mutex_lock entry_lock(entry->mu);
  if (!entry->compiled) {
  + VLOG(1) << "Compilation cache miss for signature: "
  + << SignatureDebugString(signature);
  // Do the actual JIT compilation without holding the lock (it can take
  // a long time.)
  std::vector<XlaCompiler::Argument> args;
  