Expand CRX verifier to verify CRX₃ files.

components/crx_file/BUILD.gn

 # 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("//third_party/protobuf/proto_library.gni")
+
 static_library("crx_file") {
   sources = [
     "crx2_file.cc",
     "crx2_file.h",
     "crx_verifier.cc",
     "crx_verifier.h",
     "id_util.cc",
     "id_util.h",
   ]
 
   deps = [
     "//base",
     "//crypto",
   ]
+
+  public_deps = [
+    ":crx3_proto",
+  ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
+    "crx_verifier_unittest.cc",
     "id_util_unittest.cc",
   ]
 
   deps = [
     ":crx_file",
     "//base",
     "//testing/gtest",
   ]
 }
+
+proto_library("crx3_proto") {
+  sources = [
+    "crx3.proto",
+  ]
+}