gn2bp: add back default_targets support

This will be useful as cronet consists of 4 targets.

Test: //componetns/cronet/android:cronet
Change-Id: I68d9e12607488b56b12bf65731100caeb9bdcb04
diff --git a/tools/gn2bp/gen_android_bp b/tools/gn2bp/gen_android_bp
index a864665..eba5f42 100755
--- a/tools/gn2bp/gen_android_bp
+++ b/tools/gn2bp/gen_android_bp
@@ -38,6 +38,11 @@
 
 ROOT_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 
+# Default targets to translate to the blueprint file.
+default_targets = [
+    '//components/cronet/android:cronet',
+]
+
 # Defines a custom init_rc argument to be applied to the corresponding output
 # blueprint target.
 target_initrc = {
@@ -1337,7 +1342,7 @@
     desc = json.load(f)
 
   gn = gn_utils.GnParser(desc)
-  blueprint = create_blueprint_for_targets(gn, desc, args.targets)
+  blueprint = create_blueprint_for_targets(gn, desc, args.targets or default_targets)
   project_root = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
   tool_name = os.path.relpath(os.path.abspath(__file__), project_root)