Make nanobench and dm be usable from Chromium build

bench/nanobench.h

Index: bench/nanobench.h
diff --git a/platform_tools/android/tests/inputs/SkUserConfig-h.txt b/bench/nanobench.h
similarity index 57%
copy from platform_tools/android/tests/inputs/SkUserConfig-h.txt
copy to bench/nanobench.h
index a8f97ebe1f4734cfabf486c92820914ef0f757e7..4616747382adf9f49ab11e798b7eae4fbe8b7bcc 100644
--- a/platform_tools/android/tests/inputs/SkUserConfig-h.txt
+++ b/bench/nanobench.h
@@ -4,7 +4,10 @@
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
+#ifndef nanobench_DEFINED
+#define nanobench_DEFINED
 
-/*
- *  Unchanging SkUserConfig.h for testing generate_user_config.
- */
+// API for nanobench app.
+int nanobench_main();
+
+#endif