Presentation API: implement .getAvalability() (Blink side).

Source/modules/modules.gypi

Index: Source/modules/modules.gypi
diff --git a/Source/modules/modules.gypi b/Source/modules/modules.gypi
index 0db74fc9c7c151cbcb1ac527741c25b965f4157c..0cd1d3d33cee60044038621bed580297a6dedfc3 100644
--- a/Source/modules/modules.gypi
+++ b/Source/modules/modules.gypi
@@ -147,9 +147,9 @@
       'plugins/MimeTypeArray.idl',
       'plugins/Plugin.idl',
       'plugins/PluginArray.idl',
-      'presentation/AvailableChangeEvent.idl',
       'presentation/DefaultSessionStartEvent.idl',
       'presentation/Presentation.idl',
+      'presentation/PresentationAvailability.idl',
       'presentation/PresentationSession.idl',
       'push_messaging/PushEvent.idl',
       'push_messaging/PushManager.idl',
@@ -333,7 +333,6 @@
       'mediastream/RTCIceCandidateEvent.idl',
       'navigatorconnect/CrossOriginConnectEvent.idl',
       'notifications/NotificationEvent.idl',
-      'presentation/AvailableChangeEvent.idl',
       'presentation/DefaultSessionStartEvent.idl',
       'push_messaging/PushEvent.idl',
       'serviceworkers/ExtendableEvent.idl',
@@ -390,7 +389,6 @@
       'permissions/MidiPermissionDescriptor.idl',
       'permissions/PermissionDescriptor.idl',
       'permissions/PushPermissionDescriptor.idl',
-      'presentation/AvailableChangeEventInit.idl',
       'presentation/DefaultSessionStartEventInit.idl',
       'push_messaging/PushEventInit.idl',
       'push_messaging/PushSubscriptionOptions.idl',
@@ -498,8 +496,6 @@
       '<(blink_modules_output_dir)/permissions/PermissionDescriptor.h',
       '<(blink_modules_output_dir)/permissions/PushPermissionDescriptor.cpp',
       '<(blink_modules_output_dir)/permissions/PushPermissionDescriptor.h',
-      '<(blink_modules_output_dir)/presentation/AvailableChangeEventInit.cpp',
-      '<(blink_modules_output_dir)/presentation/AvailableChangeEventInit.h',
       '<(blink_modules_output_dir)/presentation/DefaultSessionStartEventInit.cpp',
       '<(blink_modules_output_dir)/presentation/DefaultSessionStartEventInit.h',
       '<(blink_modules_output_dir)/push_messaging/PushEventInit.cpp',
@@ -1093,14 +1089,16 @@
       'plugins/NavigatorPlugins.h',
       'plugins/PluginOcclusionSupport.cpp',
       'plugins/PluginOcclusionSupport.h',
-      'presentation/AvailableChangeEvent.cpp',
-      'presentation/AvailableChangeEvent.h',
       'presentation/DefaultSessionStartEvent.cpp',
       'presentation/DefaultSessionStartEvent.h',
       'presentation/NavigatorPresentation.cpp',
       'presentation/NavigatorPresentation.h',
       'presentation/Presentation.cpp',
       'presentation/Presentation.h',
+      'presentation/PresentationAvailability.cpp',
+      'presentation/PresentationAvailability.h',
+      'presentation/PresentationAvailabilityCallback.cpp',
+      'presentation/PresentationAvailabilityCallback.h',
       'presentation/PresentationController.cpp',
       'presentation/PresentationController.h',
       'presentation/PresentationError.cpp',