gn2bp: Fix cronet build for OUT_DIR set

Follow aosp/2394536

Test: ./update_results.sh
Change-Id: I20e3fa9242957c1fc1fc79692e4275f9b52f0fc0
diff --git a/tools/gn2bp/Android.bp.swp b/tools/gn2bp/Android.bp.swp
index c881767..9f4ac7c 100644
--- a/tools/gn2bp/Android.bp.swp
+++ b/tools/gn2bp/Android.bp.swp
@@ -381,7 +381,7 @@
          "--input_file " +
          "java/lang/Runtime.class " +
          "--javap " +
-         "$$(find out/.path -name javap) " +
+         "$$(find $${OUT_DIR:-out}/.path -name javap) " +
          "--package_prefix " +
          "android.net.http.internal",
     out: [