Add retrolambda.py and integrate it to build process.

build/config/android/rules.gni

Index: build/config/android/rules.gni
diff --git a/build/config/android/rules.gni b/build/config/android/rules.gni
index 2cc550bc3dade4091a87d0af802e73299303dd0f..a74eb6c82208b93dff608ddfa4cc24383e46f6f8 100644
--- a/build/config/android/rules.gni
+++ b/build/config/android/rules.gni
@@ -1160,6 +1160,9 @@ if (enable_java_templates) {
   #     will be added to the javac classpath.
   #   jar_path: Path to the prebuilt jar.
   #   jar_dep: Target that builds jar_path (optional).
+  #   main_class: When specified, a wrapper script is created within
+  #     $root_build_dir/bin to launch the binary with the given class as the
+  #     entrypoint.
   #   output_name: File name for the output .jar (not including extension).
   #     Defaults to the input .jar file name.
   #   proguard_preprocess: If true, proguard preprocessing will be run. This can