Allows features to link to other feature splits without namespacing.

Add uses-split dependencies to AppInfo. At link time, this is used
and allows features to reference other features, before
resource namespacing is implemented in Android Studio.

bug:135681292
Test: Link_test, ReferenceLinker_test, and integration tests.
Change-Id: Ifdf0067e7370552b6b9d4d6d4713d4484b6ea154
diff --git a/tools/aapt2/AppInfo.h b/tools/aapt2/AppInfo.h
index 7512353..d3ca357 100644
--- a/tools/aapt2/AppInfo.h
+++ b/tools/aapt2/AppInfo.h
@@ -17,6 +17,7 @@
 #ifndef AAPT_APP_INFO_H
 #define AAPT_APP_INFO_H
 
+#include <set>
 #include <string>
 
 #include "util/Maybe.h"
@@ -42,6 +43,9 @@
 
   // The app's split name, if it is a split.
   Maybe<std::string> split_name;
+
+  // The split names that this split depends on.
+  std::set<std::string> split_name_dependencies;
 };
 
 }  // namespace aapt