Revert of Web MIDI: split build rules for media/midi

Revert of Web MIDI: split build rules for media/midi (patchset #19 id:340001 of https://codereview.chromium.org/1065743003/)

Reason for revert:
Very sorry to have to revert this after so much work, but midi_unittests has been consistently broken on Android Tests bot e.g. https://build.chromium.org/p/chromium.webkit/builders/Android%20Tests%20%28dbg%29/builds/25597

Original issue's description:
> Web MIDI: split build rules for media/midi
>
> Split MIDI related stuffs from media as a component in build files.
> Also, MIDI related unit tests are split into midi_unittests.
>
> BUG=475869
> TEST=git cl try
>
> Committed: https://crrev.com/31624cad1a3b5cf26950b864837ba44b3aa38331
> Cr-Commit-Position: refs/heads/master@{#326247}

TBR=phajdan.jr@chromium.org,dalecurtis@chromium.org,dpranke@chromium.org,boliu@chromium.org,damienv@chromium.org,jam@chromium.org,thestig@chromium.org,lcwu@chromium.org,gunsch@chromium.org,toyoshim@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=475869
Committed: https://crrev.com/60006f2c430e17fc8338ff370a1c88cdc61b7f07
Cr-Commit-Position: refs/heads/master@{#326343}

[aboxhall, 2015-04-22 18:22:43]

Created Revert of Web MIDI: split build rules for media/midi

[commit-bot: I haz the power, 2015-04-22 18:25:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1085843003/1

[commit-bot: I haz the power, 2015-04-22 18:28:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-22 18:28:57]

Patchset 1 (id:??) landed as
https://crrev.com/60006f2c430e17fc8338ff370a1c88cdc61b7f07
Cr-Commit-Position: refs/heads/master@{#326343}