gn2bp: add .java to supported source files

Test: //base:base
Change-Id: Ie84b8777c045aea0d5447f24e148cbcf75b339fc
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index 8646209..ee092db 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -467,7 +467,7 @@
 
 def is_supported_source_file(name):
   """Returns True if |name| can appear in a 'srcs' list."""
-  return os.path.splitext(name)[1] in ['.c', '.cc', '.proto']
+  return os.path.splitext(name)[1] in ['.c', '.cc', '.java', '.proto']
 
 
 def create_proto_modules(blueprint, gn, target):