Added automatic mode to FakeInputAudioStream to generate automatic beeps.

This patch is to allow writing audio only tests using the fake input stream, also it changes the name of the fake device from "Default" to "Fake Audio, which I hope it will make things less confusing.

TBR=dalecurtis@chromium.org
NOTRY=true

BUG=358541
TEST=bots existing webrtc tests.

Review URL: https://codereview.chromium.org/272723006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269354 0039d316-1c4b-4281-b951-d872f2087c98

• content/browser/renderer_host/media/audio_input_device_manager.cc[diff]
• content/browser/renderer_host/media/audio_input_device_manager.h[diff]
• content/browser/renderer_host/media/audio_input_device_manager_unittest.cc[diff]
• content/browser/renderer_host/media/media_stream_dispatcher_host_unittest.cc[diff]
• media/audio/fake_audio_input_stream.cc[diff]
• media/audio/fake_audio_input_stream.h[diff]
• media/audio/mock_audio_manager.cc[diff]