GN + Android: extract android_standalone_library rule.

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 5d0cb372388f729608e30c4c27e8dec2b8415e0d..09ec580e635c1bccca039b153bf48774448ed660 100644
--- a/build/config/android/rules.gni
+++ b/build/config/android/rules.gni
@@ -922,8 +922,6 @@ template("java_prebuilt") {
 #
 #   dex_path: If set, the resulting .dex.jar file will be placed under this
 #     path.
-#   standalone_dex_path: If set, a standalone .dex.jar containing the code from
-#     the library and all dependencies will be placed under this path.
 #
 #
 # Example
@@ -986,9 +984,6 @@ template("android_library") {
     if (defined(invoker.dex_path)) {
       dex_path = invoker.dex_path
     }
-    if (defined(invoker.standalone_dex_path)) {
-      standalone_dex_path = invoker.standalone_dex_path
-    }
 
     supports_android = true
     requires_android = true
@@ -1005,6 +1000,27 @@ template("android_library") {
   }
 }
 
+# Declare an Android library that packages its dependencies into a single
+# .dex.jar.
+#
+# Variables
+#   deps: specifies the dependencies of this target. Android libraries and
+#     resources in deps will be packaged into the resulting .dex.jar file.
+#   standalone_dex_path: optional override for the output file location.
+template("android_standalone_library") {
+  java_library_impl(target_name) {
+    deps = invoker.deps
+    if (defined(invoker.standalone_dex_path)) {
+      standalone_dex_path = invoker.standalone_dex_path
+    } else {
+      standalone_dex_path = "$target_out_dir/$target_name.dex.jar"
+    }
+
+    supports_android = true
+    requires_android = true
+  }
+}
+
 # Declare an Android library target for a prebuilt jar
 #
 # This target creates an Android library containing java code and Android