[android] Write a runner script to the top-level output dir for gtests.

build/config/android/internal_rules.gni

Index: build/config/android/internal_rules.gni
diff --git a/build/config/android/internal_rules.gni b/build/config/android/internal_rules.gni
index 218fdfc97771e1fa9f99e7c7623350c9722cc8f7..813686305c03adcaa679923f6c559c0b866a43ee 100644
--- a/build/config/android/internal_rules.gni
+++ b/build/config/android/internal_rules.gni
@@ -615,7 +615,12 @@ template("test_runner_script") {
       test_runner_args += [ "--tool=asan" ]
     }
 
-    generated_script = "$root_build_dir/bin/run_${_test_name}"
+    if (defined(invoker.generated_script)) {
+      assert(_test_name != "" || true)  # Mark _test_name as used.
+      generated_script = invoker.generated_script
+    } else {
+      generated_script = "$root_build_dir/bin/run_${_test_name}"
+    }
     outputs = [
       generated_script,
     ]