Break out WebAudio suspension code into new class. Add tests.

media/base/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/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/config/linux/pkg_config.gni")
 import("//media/media_options.gni")
@@ skipping 180 matching lines @@
     "renderer.h",
     "renderer_client.h",
     "renderer_factory.cc",
     "renderer_factory.h",
     "sample_format.cc",
     "sample_format.h",
     "seekable_buffer.cc",
     "seekable_buffer.h",
     "serial_runner.cc",
     "serial_runner.h",
+    "silent_sink_suspender.cc",
+    "silent_sink_suspender.h",
     "simd/convert_rgb_to_yuv.h",
     "simd/convert_rgb_to_yuv_c.cc",
     "simd/convert_yuv_to_rgb.h",
     "simd/convert_yuv_to_rgb_c.cc",
     "simd/filter_yuv.h",
     "simd/filter_yuv_c.cc",
     "sinc_resampler.cc",
     "sinc_resampler.h",
     "stream_parser.cc",
     "stream_parser.h",
@@ skipping 211 matching lines @@
     "media_url_demuxer_unittest.cc",
     "mime_util_unittest.cc",
     "moving_average_unittest.cc",
     "multi_channel_resampler_unittest.cc",
     "null_video_sink_unittest.cc",
     "pipeline_impl_unittest.cc",
     "ranges_unittest.cc",
     "run_all_unittests.cc",
     "seekable_buffer_unittest.cc",
     "serial_runner_unittest.cc",
+    "silent_sink_suspender_unittest.cc",
     "sinc_resampler_unittest.cc",
     "stream_parser_unittest.cc",
     "text_ranges_unittest.cc",
     "text_renderer_unittest.cc",
     "time_delta_interpolator_unittest.cc",
     "user_input_monitor_unittest.cc",
     "vector_math_unittest.cc",
     "video_codecs_unittest.cc",
     "video_decoder_config_unittest.cc",
     "video_frame_pool_unittest.cc",
@@ skipping 139 matching lines @@
 
 fuzzer_test("media_container_names_fuzzer") {
   sources = [
     "container_names_fuzzertest.cc",
   ]
   deps = [
     "//base",
     "//media",
   ]
 }