Add fake for InstanceIDWithSubtype.java, in order to re-use unit test

components/gcm_driver/instance_id/android/BUILD.gn

Index: components/gcm_driver/instance_id/android/BUILD.gn
diff --git a/components/gcm_driver/instance_id/android/BUILD.gn b/components/gcm_driver/instance_id/android/BUILD.gn
index 6168aff07e3d74d1a772b415696eb60e19c2e6c0..9d980403b92aa5c4c75467ec79936fd4b74482d0 100644
--- a/components/gcm_driver/instance_id/android/BUILD.gn
+++ b/components/gcm_driver/instance_id/android/BUILD.gn
@@ -12,6 +12,14 @@ generate_jni("jni_headers") {
   jni_package = "components/gcm_driver/instance_id"
 }
 
+# GYP version: components/gcm_driver.gypi:instance_id_driver_test_support_jni_headers
+generate_jni("test_support_jni_headers") {
+  sources = [
+    "javatests/src/org/chromium/components/gcm_driver/instance_id/FakeInstanceIDWithSubtype.java",
+  ]
+  jni_package = "components/gcm_driver/instance_id"
+}
+
 # GYP version: components/gcm_driver.gypi:instance_id_driver_java
 android_library("instance_id_driver_java") {
   deps = [
@@ -24,3 +32,14 @@ android_library("instance_id_driver_java") {
     "java/src/org/chromium/components/gcm_driver/instance_id/InstanceIDWithSubtype.java",
   ]
 }
+
+# GYP version: components/gcm_driver.gypi:instance_id_driver_test_support_java
+android_library("instance_id_driver_test_support_java") {
+  deps = [
+    ":instance_id_driver_java",
+    "//base:base_java",
+    google_play_services_library,
+  ]
+
+  java_files = [ "javatests/src/org/chromium/components/gcm_driver/instance_id/FakeInstanceIDWithSubtype.java" ]
+}