Move iOS image_fetcher::ImageDecoder to layered component

components/image_fetcher/ios/BUILD.gn

 # Copyright 2017 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("ios") {
   sources = [
     "ios_image_data_fetcher_wrapper.h",
     "ios_image_data_fetcher_wrapper.mm",
+    "ios_image_decoder_impl.h",
+    "ios_image_decoder_impl.mm",
     "webp_decoder.h",
     "webp_decoder.mm",
   ]
   deps = [
     "//base",
     "//components/image_fetcher",
+    "//ios/web",
     "//net",
     "//third_party/libwebp:libwebp_dec",
+    "//ui/gfx",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "ios_image_data_fetcher_wrapper_unittest.mm",
+    "ios_image_decoder_impl_unittest.mm",
     "webp_decoder_unittest.mm",
   ]
   deps = [
     ":ios",
     ":webp_transcode_unit_tests_bundle_data",
     "//base",
     "//net",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
+    "//ui/gfx",
   ]
   configs += [ "//build/config/compiler:enable_arc" ]
 }
 
 bundle_data("webp_transcode_unit_tests_bundle_data") {
   visibility = [ ":unit_tests" ]
   testonly = true
   sources = [
     "//components/test/data/webp_transcode/test.jpg",
     "//components/test/data/webp_transcode/test.webp",
     "//components/test/data/webp_transcode/test_alpha.png",
     "//components/test/data/webp_transcode/test_alpha.webp",
     "//components/test/data/webp_transcode/test_small.tiff",
     "//components/test/data/webp_transcode/test_small.webp",
   ]
   outputs = [
     "{{bundle_resources_dir}}/{{source_root_relative_dir}}/" +
         "{{source_file_part}}",
   ]
 }