Implement WebM subsample support

media/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("//build/buildflag_header.gni")
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/features.gni")
 import("//build/config/linux/pkg_config.gni")
 import("//build/config/ui.gni")
@@ skipping 547 matching lines @@
     "filters/vp9_raw_bits_reader_unittest.cc",
     "formats/common/offset_byte_queue_unittest.cc",
     "formats/webm/cluster_builder.cc",
     "formats/webm/cluster_builder.h",
     "formats/webm/opus_packet_builder.cc",
     "formats/webm/opus_packet_builder.h",
     "formats/webm/tracks_builder.cc",
     "formats/webm/tracks_builder.h",
     "formats/webm/webm_cluster_parser_unittest.cc",
     "formats/webm/webm_content_encodings_client_unittest.cc",
+    "formats/webm/webm_crypto_helpers_unittest.cc",
     "formats/webm/webm_parser_unittest.cc",
     "formats/webm/webm_stream_parser_unittest.cc",
     "formats/webm/webm_tracks_parser_unittest.cc",
     "formats/webm/webm_webvtt_parser_unittest.cc",
     "muxers/webm_muxer_unittest.cc",
     "renderers/audio_renderer_impl_unittest.cc",
     "renderers/renderer_impl_unittest.cc",
     "renderers/skcanvas_video_renderer_unittest.cc",
     "renderers/video_renderer_impl_unittest.cc",
     "video/gpu_memory_buffer_video_frame_pool_unittest.cc",
@@ skipping 321 matching lines @@
 fuzzer_test("media_webm_muxer_fuzzer") {
   sources = [
     "muxers/webm_muxer_fuzzertest.cc",
   ]
   deps = [
     ":media",
     "//base",
     "//third_party/libwebm",
   ]
 }