[NOT FOR COMMIT] Added GN support for Android .AAR packaged libraries

build/config/android/rules.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/android/config.gni")
 import("//build/config/android/internal_rules.gni")
 import("//build/toolchain/toolchain.gni")
 
 assert(is_android)
 
@@ skipping 2479 matching lines @@
 
     android_library(target_name) {
       chromium_code = false
       java_files = []
       srcjar_deps = [ ":${_template_name}__protoc_java" ]
       deps = [
         "//third_party/android_protobuf:protobuf_nano_javalib",
       ]
     }
   }
+
+  # Declare an Android library target for a prebuilt aar
+  #
+  # This target creates an Android library containing java code and Android
+  # resources.
+  #
+  # Variables
+  #   aar_path: Path to the aar.
+  #   custom_package: Custom package name to be used for the resource
+  #     directory.
+  #   skip_jar: If true do not include classes.jar
+  #   skip_res: If true do not include the resource directory
+  #
+  # Example
+  #   android_aar_prebuilt("foo_aar") {
+  #     aar_path = "foo.aar"
+  #   }
+  template("android_aar_prebuilt") {
+    set_sources_assignment_filter([])

[agrieve, 2016/06/16 02:00:04]

no need for this since you aren't using "sources" as an arg.

+
+    assert(defined(invoker.aar_path))
+
+    build_config = "${root_out_dir}/${target_name}.build_config"
+
+    _output_path = "${root_out_dir}/unpacked_aar/${target_name}"
+    _copied_aar_path = "${_output_path}/${target_name}.aar"
+
+    _unpack_target_name = "${target_name}__unpack_aar"
+    _copy_target_name = "${target_name}__copy"
+
+    action(_unpack_target_name) {
+      script = "//build/config/android/unpack_aar.py"  # Unzips the AAR
+      args = [
+        rebase_path(invoker.aar_path, root_build_dir),
+        rebase_path(_output_path, root_build_dir),
+      ]
+      outputs = [
+        "${_output_path}/AndroidManifest.xml",
+        "${_output_path}/classes.jar",
+        "${_output_path}/R.txt",
+      ]
+    }
+
+    copy(_copy_target_name) {

[agrieve, 2016/06/16 02:00:04]

Why copy it?

+      sources = [
+        rebase_path(invoker.aar_path, root_build_dir),
+      ]
+      outputs = [
+        _copied_aar_path,
+      ]
+    }
+
+    write_build_config(target_name) {
+      deps = [
+        ":$_copy_target_name",
+        ":$_unpack_target_name",
+      ]
+
+      type = "android_aar"
+      jar_path = "${_output_path}/classes.jar"
+      r_text = "${_output_path}/R.txt"
+      resources_zip = _copied_aar_path
+    }
+  }
 }