Add Robolectric build and license files to third_party.

third_party/robolectric/BUILD.gn

Index: third_party/robolectric/BUILD.gn
diff --git a/third_party/robolectric/BUILD.gn b/third_party/robolectric/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..302bde1b89cd16c068de7c6fc5ba73f29c506350
--- /dev/null
+++ b/third_party/robolectric/BUILD.gn
@@ -0,0 +1,19 @@
+# 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/rules.gni")
+
+# GYP: //third_party/robolectric/robolectric.gyp:android_all_jar
+java_prebuilt("android_all_java") {
+  jar_path = "lib/android-all-5.0.0_r2-robolectric-0.jar"
+}
+
+# GYP: //third_party/robolectric/robolectric.gyp:robolectric_jar
+java_prebuilt("robolectric_java") {
+  testonly = true
+  jar_path = "lib/robolectric-2.4-jar-with-dependencies.jar"
+  deps = [
+    ":android_all_java",
+  ]
+}