Fix android depfiles to always list GN's outputs[0]

components/cronet/android/BUILD.gn

Index: components/cronet/android/BUILD.gn
diff --git a/components/cronet/android/BUILD.gn b/components/cronet/android/BUILD.gn
index cde4b92cec31a091cd97fd541b8e2e0aa2806ffb..973642984ad7636f0de79a2f69bd77bca30f2917 100644
--- a/components/cronet/android/BUILD.gn
+++ b/components/cronet/android/BUILD.gn
@@ -872,8 +872,9 @@ action("generate_licenses") {
 action("generate_javadoc") {
   script = "//components/cronet/tools/generate_javadoc.py"
   depfile = "$target_gen_dir/$target_name.d"
+  _stamp_file = "$target_gen_dir/$target_name.stamp"
   outputs = [
-    depfile,
+    _stamp_file,
   ]
   args = [
     "--output-dir",
@@ -886,6 +887,8 @@ action("generate_javadoc") {
     rebase_path("//components/cronet/README.md", root_build_dir),
     "--depfile",
     rebase_path(depfile, root_build_dir),
+    "--stamp",
+    rebase_path(_stamp_file, root_build_dir),
     "--lib-java-dir",
     rebase_path("$root_build_dir/lib.java/components/cronet/android",
                 root_build_dir),