message: Update naming of MLIR bridge flag and add some documentation.
diff: @@ -167,8 +167,16 @@ void AllocateAndParseFlags() {
  jitter_flags = new IntroduceFloatingPointJitterPassFlags;
  jitter_flags->jitter_amount = 1e-5;
  + // The `enable_mlir_bridge` flag allows the user to explicitly request that
  + // their program is (or isn't) compiled using the MLIR-based TF-to-XLA bridge.
  + //
  + // The `enable_mlir_bridge_is_explicit` variable tracks whether or not the
  + // user has made an explicit request. That is, if this variable is set to
  + // true, the program honors the user's request as per `enable_mlir_bridge`; if
  + // it's set to false, the default behavior is used (which may run either
  + // bridge, on a per-graph basis).
  bool enable_mlir_bridge = false;
  - bool enable_mlir_bridge_flag_updated = false;
  + bool enable_mlir_bridge_is_explicit = false;
  auto setter_for_jitter_tensor_names = [](string sequence) {
  jitter_flags->tensor_names = absl::StrSplit(sequence, ',');
  @@ -219,13 +227,13 @@ void AllocateAndParseFlags() {
  Flag("tf_mlir_enable_mlir_bridge", &enable_mlir_bridge,
  "Enables experimental MLIR-Based TensorFlow Compiler Bridge.",
  - &enable_mlir_bridge_flag_updated)});
  + &enable_mlir_bridge_is_explicit)});
  AppendMarkForCompilationPassFlagsInternal(flag_list);
  xla::ParseFlagsFromEnvAndDieIfUnknown("TF_XLA_FLAGS", *flag_list);
  mlir_flags = new MlirCommonFlags;
  - if (!enable_mlir_bridge_flag_updated) {
  + if (!enable_mlir_bridge_is_explicit) {
  mlir_flags->tf_mlir_enable_mlir_bridge =
  ConfigProto::Experimental::MLIR_BRIDGE_ROLLOUT_UNSPECIFIED;
  } else if (enable_mlir_bridge) {
  