Add an api_files property in java_api_library

java_api_contribution is useful to java_api_library when the api files
are not colocated.

If they are colocated (e.g. in Multi-tree assembled api_surfaces
directory), it is useful to refer to them directly without nedding to
create a java_api_contribution module.

Test: In build/soong, go test ./java
Change-Id: I5b4e557068a1e5c71a80c76452030e72ec83a696
diff --git a/java/java.go b/java/java.go
index e37a77e..9dd5850 100644
--- a/java/java.go
+++ b/java/java.go
@@ -1567,8 +1567,14 @@
 	Api_surface *string
 
 	// list of Java API contribution modules that consists this API surface
+	// This is a list of Soong modules
 	Api_contributions []string
 
+	// list of api.txt files relative to this directory that contribute to the
+	// API surface.
+	// This is a list of relative paths
+	Api_files []string
+
 	// List of flags to be passed to the javac compiler to generate jar file
 	Javacflags []string
 }
@@ -1665,6 +1671,13 @@
 		srcFiles = append(srcFiles, android.PathForSource(ctx, provider.ApiFile.String()))
 	})
 
+	// Add the api_files inputs
+	for _, api := range al.properties.Api_files {
+		// Use MaybeExistentPathForSource since the api file might not exist during analysis.
+		// This will be provided by the orchestrator in the combined execution.
+		srcFiles = append(srcFiles, android.MaybeExistentPathForSource(ctx, ctx.ModuleDir(), api))
+	}
+
 	cmd := metalavaStubCmd(ctx, rule, srcFiles, homeDir)
 
 	al.stubsFlags(ctx, cmd, stubsDir)