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

Review URL: https://codereview.chromium.org/1085843003

Cr-Commit-Position: refs/heads/master@{#326343}

• BUILD.gn[diff]
• android_webview/android_webview.gyp[diff]
• build/all.gyp[diff]
• build/android/pylib/gtest/gtest_config.py[diff]
• build/android/pylib/gtest/setup.py[diff]
• build/gn_migration.gypi[diff]
• chromecast/chromecast_tests.gypi[diff]
• content/app/DEPS[diff]
• content/app/android/library_loader_hooks.cc[diff]
• content/common/BUILD.gn[diff]
• content/content_common.gypi[diff]
• content/content_tests.gypi[diff]
• media/BUILD.gn[diff]
• media/OWNERS[diff]
• media/base/android/BUILD.gn[diff]
• media/base/android/java/src/org/chromium/media/UsbMidiDeviceAndroid.java[Renamed from media/midi/java/src/org/chromium/media/midi/UsbMidiDeviceAndroid.java - diff]
• media/base/android/java/src/org/chromium/media/UsbMidiDeviceFactoryAndroid.java[Renamed from media/midi/java/src/org/chromium/media/midi/UsbMidiDeviceFactoryAndroid.java - diff]
• media/base/android/media_jni_registrar.cc[diff]
• media/media.gyp[diff]
• media/midi/BUILD.gn[Deleted - diff]
• media/midi/midi.gyp[Deleted - diff]
• media/midi/midi_jni_registrar.cc[Deleted - diff]
• media/midi/midi_jni_registrar.h[Deleted - diff]
• media/midi/midi_manager_usb.cc[diff]
• media/midi/midi_manager_win.cc[diff]
• media/midi/midi_scheduler.h[diff]
• media/midi/midi_unittests.isolate[Deleted - diff]
• media/midi/usb_midi_device_android.cc[diff]
• media/midi/usb_midi_device_factory_android.cc[diff]
• media/midi/usb_midi_output_stream.cc[diff]
• testing/buildbot/chromium.chromiumos.json[diff]
• testing/buildbot/chromium.fyi.json[diff]
• testing/buildbot/chromium.linux.json[diff]
• testing/buildbot/chromium.mac.json[diff]
• testing/buildbot/chromium.memory.fyi.json[diff]
• testing/buildbot/chromium.memory.json[diff]
• testing/buildbot/chromium.webkit.json[diff]
• testing/buildbot/chromium.win.json[diff]
• testing/buildbot/chromium_memory_trybot.json[diff]
• testing/buildbot/chromium_trybot.json[diff]
• tools/valgrind/chrome_tests.py[diff]