Replace Maybe with std::optional

With c++17, std::optional provides the functionality that Maybe
provided.

Bug: 183215655
Test: aapt2_tests
Change-Id: I62bb9c2fa4985dc5217a6ed153df92b85ad9a034
diff --git a/tools/aapt2/cmd/Compile.h b/tools/aapt2/cmd/Compile.h
index 1bc1f66..bd2e3d7 100644
--- a/tools/aapt2/cmd/Compile.h
+++ b/tools/aapt2/cmd/Compile.h
@@ -17,7 +17,10 @@
 #ifndef AAPT2_COMPILE_H
 #define AAPT2_COMPILE_H
 
-#include "androidfw/StringPiece.h"
+#include <optional>
+
+#include <androidfw/StringPiece.h>
+
 #include "format/Archive.h"
 #include "process/IResourceTableConsumer.h"
 #include "Command.h"
@@ -28,11 +31,11 @@
 
 struct CompileOptions {
   std::string output_path;
-  Maybe<std::string> source_path;
-  Maybe<std::string> res_dir;
-  Maybe<std::string> res_zip;
-  Maybe<std::string> generate_text_symbols_path;
-  Maybe<Visibility::Level> visibility;
+  std::optional<std::string> source_path;
+  std::optional<std::string> res_dir;
+  std::optional<std::string> res_zip;
+  std::optional<std::string> generate_text_symbols_path;
+  std::optional<Visibility::Level> visibility;
   bool pseudolocalize = false;
   bool no_png_crunch = false;
   bool legacy_mode = false;
@@ -80,8 +83,8 @@
  private:
   IDiagnostics* diagnostic_;
   CompileOptions options_;
-  Maybe<std::string> visibility_;
-  Maybe<std::string> trace_folder_;
+  std::optional<std::string> visibility_;
+  std::optional<std::string> trace_folder_;
 };
 
 int Compile(IAaptContext* context, io::IFileCollection* inputs, IArchiveWriter* output_writer,