message: Make logging less verbose
  I want --vmodule=xla_compilation_cache=1 to print only the most essential
  things.
diff: @@ -259,7 +259,7 @@ Status XlaCompilationCache::CompileImpl(
  const XlaCompiler::CompileOptions& compile_options,
  bool compile_single_op) {
  CHECK_NE(executable, nullptr);
  - VLOG(1) << "XlaCompilationCache::Compile " << DebugString();
  + VLOG(2) << "XlaCompilationCache::Compile " << DebugString();
  if (VLOG_IS_ON(2)) {
  VLOG(2) << "num_inputs=" << ctx->num_inputs()
  @@ -310,7 +310,7 @@ Status XlaCompilationCache::CompileImpl(
  // cache eviction.
  mutex_lock entry_lock(entry->mu);
  if (!entry->compiled) {
  - VLOG(1) << "Compilation cache miss for signature: "
  + VLOG(2) << "Compilation cache miss for signature: "
  << SignatureDebugString(signature);
  tensorflow::Env* env = tensorflow::Env::Default();
  const uint64 compile_start_us = env->NowMicros();
  