Add a parser for messages with a Web Push Protocol-based payload

components/gcm_driver/crypto/BUILD.gn

Index: components/gcm_driver/crypto/BUILD.gn
diff --git a/components/gcm_driver/crypto/BUILD.gn b/components/gcm_driver/crypto/BUILD.gn
index 62aa717931245cb3ddfa9c3ec5d722ec18160709..20d24ee5f85cfa0f5b1fc94745eb05c5450acd69 100644
--- a/components/gcm_driver/crypto/BUILD.gn
+++ b/components/gcm_driver/crypto/BUILD.gn
@@ -14,6 +14,8 @@ static_library("crypto") {
     "gcm_key_store.h",
     "gcm_message_cryptographer.cc",
     "gcm_message_cryptographer.h",
+    "message_payload_parser.cc",
+    "message_payload_parser.h",
     "p256_key_util.cc",
     "p256_key_util.h",
   ]
@@ -52,6 +54,7 @@ source_set("unit_tests") {
     "gcm_encryption_provider_unittest.cc",
     "gcm_key_store_unittest.cc",
     "gcm_message_cryptographer_unittest.cc",
+    "message_payload_parser_unittest.cc",
     "p256_key_util_unittest.cc",
   ]