Make AudioDebugFileWriter create its own file worker thread.

Remove the task_runner from AudioDebugFileWriter's constructor and make it
use the new TaskScheduler API.

TaskRunners shouldn't be passed through several components. Instead, the
component that uses a TaskRunner should be the one that creates it.

The main change of this CL is in media/audio/audio_debug_file_writer.h, the
rest is mostly plumbing.

[email protected]
BUG=689520
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2885173002
Cr-Commit-Position: refs/heads/master@{#473690}
24 files changed