Teach the GCM Driver how to decrypt incoming messages.

components/gcm_driver/crypto/BUILD.gn

 # Copyright 2015 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/crypto.gni")
 
 # GYP version: components/gcm_driver.gypi:gcm_driver_crypto
 source_set("crypto") {
   sources = [
     "encryption_header_parsers.cc",
@@ skipping 21 matching lines @@
     sources -= [ "gcm_message_cryptographer_nss.cc" ]
   } else {
     sources -= [ "gcm_message_cryptographer_openssl.cc" ]
   }
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "encryption_header_parsers_unittest.cc",
+    "gcm_encryption_provider_unittest.cc",
     "gcm_key_store_unittest.cc",
     "gcm_message_cryptographer_unittest.cc",
   ]
 
   deps = [
     ":crypto",
     "//base",
     "//crypto:platform",
     "//testing/gtest",
     "//third_party/protobuf:protobuf_lite",
   ]
 }