Track sources for srcjars across modules

Robolectric coverage needs a srcjar that sometimes needs to
include sources of dependencies.  Track the arguments and
dependencies necessary to jar the sources.

Test: TestIncludeSrcs
Change-Id: I9979d2b8350923a2237e743c232e6e548f54ba3b
diff --git a/java/aar.go b/java/aar.go
index 5e1f88e..7332e76 100644
--- a/java/aar.go
+++ b/java/aar.go
@@ -647,6 +647,10 @@
 	return nil
 }
 
+func (a *AARImport) SrcJarArgs() ([]string, android.Paths) {
+	return nil, nil
+}
+
 var _ android.PrebuiltInterface = (*Import)(nil)
 
 // android_library_import imports an `.aar` file into the build graph as if it was built with android_library.