I have a patch for this ready in my local git working tree.
But it builds on top of several not-yet-committed CLs that would come before it, so I cannot publish a CL for it just yet.

As a follow-up, we would like to have the same thing in the media::VideoCaptureDeviceFactory API.
See crbug.com/665065

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f6995b002a218dff4841cd1793f79d4e8a8991ad

commit f6995b002a218dff4841cd1793f79d4e8a8991ad
Author: chfremer <chfremer@chromium.org>
Date: Tue Nov 15 01:00:59 2016

[Mojo Video Capture] Use string keys instead of VideoCaptureDeviceDescriptor

In interface VideoCaptureDeviceFactory, instances of struct VideoCaptureDeviceDescriptor were
used as keys for accessing capture devices. This CL simplifies this key to a simple string.

This CL is part of the Mojo Video Capture work. For the bigger picture,
see [1] CL1.9.4

BUG= 637439 , 584797
TEST=video_capture_unittests, content_unittests, capture_unittests

[1] https://docs.google.com/a/chromium.org/document/d/1Qw7rw1AJy0QHXjha36jZNiEuxsxWslJ_X-zpOhijvI8/edit?usp=sharing

yzshen@: PTAL
mcasas@: PTAL

Review-Url: https://codereview.chromium.org/2494033004
Cr-Commit-Position: refs/heads/master@{#432040}

[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/media/capture/video/video_capture_device_factory.h
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/device_factory_media_to_mojo_adapter.cc
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/device_factory_media_to_mojo_adapter.h
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/fake_device_descriptor_unittest.cc
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/fake_device_test.cc
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/fake_device_unittest.cc
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/mock_device_descriptor_receiver.h
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/mock_device_test.cc
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/public/interfaces/video_capture_device_factory.mojom
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/receiver_mojo_to_media_adapter.h
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/video_capture_service.cc
[modify] https://crrev.com/f6995b002a218dff4841cd1793f79d4e8a8991ad/services/video_capture/video_capture_service_unittest.cc