Port //components/webp_transcode to build with gn.

components/webp_transcode/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.
+
+source_set("webp_transcode") {
+  sources = [
+    "webp_decoder.h",
+    "webp_decoder.mm",
+    "webp_network_client.h",
+    "webp_network_client.mm",
+    "webp_network_client_factory.h",
+    "webp_network_client_factory.mm",
+  ]
+
+  deps = [
+    "//base",
+    "//ios/net",
+    "//net",
+    "//third_party/libwebp:libwebp_dec",
+  ]
+}
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "webp_decoder_unittest.mm",
+    "webp_network_client_unittest.mm",
+  ]
+
+  deps = [
+    "//base",
+    "//net",
+    "//testing/gmock",
+    "//testing/gtest",
+    "//third_party/ocmock",
+    ":webp_transcode",
+  ]
+}