Support $(location...) in droiddoc_options

Adds droiddoc_option_files property which are passed through to
droiddoc's arg_files property.

Bug: 124220029
Test: make checkbuild
Change-Id: I6e98752cebeaac5a8779e04e6c804763c177e354
diff --git a/java/sdk_library.go b/java/sdk_library.go
index 85ce533..3623e7c 100644
--- a/java/sdk_library.go
+++ b/java/sdk_library.go
@@ -100,7 +100,13 @@
 	// list of package names that must be hidden from the API
 	Hidden_api_packages []string
 
-	// Additional droiddoc options
+	// local files that are used within user customized droiddoc options.
+	Droiddoc_option_files []string
+
+	// additional droiddoc options
+	// Available variables for substitution:
+	//
+	//  $(location <label>): the path to the droiddoc_option_files with name <label>
 	Droiddoc_options []string
 
 	// the java library (in classpath) for documentation that provides java srcs and srcjars.
@@ -434,6 +440,7 @@
 		Srcs_lib_whitelist_dirs          []string
 		Srcs_lib_whitelist_pkgs          []string
 		Libs                             []string
+		Arg_files                        []string
 		Args                             *string
 		Api_tag_name                     *string
 		Api_filename                     *string
@@ -481,6 +488,7 @@
 	case apiScopeTest:
 		droiddocArgs = droiddocArgs + " -showAnnotation android.annotation.TestApi"
 	}
+	props.Arg_files = module.sdkLibraryProperties.Droiddoc_option_files
 	props.Args = proptools.StringPtr(droiddocArgs)
 
 	// List of APIs identified from the provided source files are created. They are later