Add a sample plugin to demonstrate the mute plugin API.

Add a sample plugin to demonstrate the mute plugin API.
https://bugs.webkit.org/show_bug.cgi?id=139231

Reviewed by Anders Carlsson.

* NetscapeMuteAPIPlugin/AudioPlayer.h: Added.
* NetscapeMuteAPIPlugin/AudioPlayer.mm: Added.
(-[AudioPlayer initWithURL:]):
(-[AudioPlayer dealloc]):
(-[AudioPlayer isReadyToPlay]):
(-[AudioPlayer isPlaying]):
(-[AudioPlayer setPlaying:]):
(-[AudioPlayer isMuted]):
(-[AudioPlayer setMuted:]):
(-[AudioPlayer observeValueForKeyPath:ofObject:change:context:]):
* NetscapeMuteAPIPlugin/English.lproj/InfoPlist.strings: Added.
* NetscapeMuteAPIPlugin/Info.plist: Added.
* NetscapeMuteAPIPlugin/MenuHandler.h: Added.
* NetscapeMuteAPIPlugin/MenuHandler.m: Added.
(-[MenuHandler _play:]):
(-[MenuHandler _pause:]):
(-[MenuHandler validateUserInterfaceItem:]):
(-[MenuHandler initWithAudioPlayer:]):
(-[MenuHandler dealloc]):
(-[MenuHandler menu]):
* NetscapeMuteAPIPlugin/NetscapeMuteAPIPlugin.xcodeproj/project.pbxproj: Added.
* NetscapeMuteAPIPlugin/main.m: Added.
(-[PluginObject initWithNPP:audioURL:]):
(-[PluginObject dealloc]):
(-[PluginObject menuHandler]):
(-[PluginObject isPlayingAudio]):
(-[PluginObject isMuted]):
(-[PluginObject setMuted:]):
(-[PluginObject readyStateDidChangeForAudioPlayer:]):
(-[PluginObject mutedStateDidChangeForAudioPlayer:]):
(-[PluginObject playStateDidChangeForAudioPlayer:]):
(-[PluginObject _invalidateDisplayString]):
(NP_Initialize):
(NP_GetEntryPoints):
(NP_Shutdown):
(NPP_New):
(NPP_Destroy):
(NPP_SetWindow):
(NPP_NewStream):
(NPP_DestroyStream):
(NPP_WriteReady):
(NPP_Write):
(NPP_StreamAsFile):
(NPP_Print):
(handleDraw):
(invalidatePlugin):
(handleMouseEvent):
(NPP_HandleEvent):
(NPP_URLNotify):
(NPP_GetValue):
(NPP_SetValue):
* NetscapeMuteAPIPlugin/test.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@176785 268f45cc-cd09-0410-ab3c-d52691b4dbfc