Bug 1797020 - Add an API to determine if there are any midi devices. r=gsvelto

Differential Revision: https://phabricator.services.mozilla.com/D160974

dom/midi/MIDIPlatformService.h

@@ -97,6 +97,9 @@ class MIDIPlatformService {
   // before/at now, and schedules MIDI Port connection closing.
   void Close(MIDIPortParent* aPort);
 
+  // Returns whether there are currently any MIDI devices.
+  bool HasDevice() { return !mPortInfo.IsEmpty(); }
+
  protected:
   MIDIPlatformService();
   virtual ~MIDIPlatformService();

ipc/glue/BackgroundParentImpl.cpp

@@ -1259,6 +1259,16 @@ bool BackgroundParentImpl::DeallocPMIDIManagerParent(
   return true;
 }
 
+mozilla::ipc::IPCResult BackgroundParentImpl::RecvHasMIDIDevice(
+    HasMIDIDeviceResolver&& aResolver) {
+  AssertIsInMainOrSocketProcess();
+  AssertIsOnBackgroundThread();
+
+  bool hasDevice = MIDIPlatformService::Get()->HasDevice();
+  aResolver(hasDevice);
+  return IPC_OK();
+}
+
 mozilla::dom::PClientManagerParent*
 BackgroundParentImpl::AllocPClientManagerParent() {
   return mozilla::dom::AllocClientManagerParent();

ipc/glue/BackgroundParentImpl.h

@@ -347,6 +347,9 @@ class BackgroundParentImpl : public PBackgroundParent {
 
   bool DeallocPMIDIManagerParent(PMIDIManagerParent* aActor) override;
 
+  mozilla::ipc::IPCResult RecvHasMIDIDevice(
+      HasMIDIDeviceResolver&& aResolver) override;
+
   mozilla::ipc::IPCResult RecvStorageActivity(
       const PrincipalInfo& aPrincipalInfo) override;
 

ipc/glue/PBackground.ipdl

@@ -254,6 +254,7 @@ parent:
 
   async PMIDIManager();
   async PMIDIPort(MIDIPortInfo portInfo, bool sysexEnabled);
+  async HasMIDIDevice() returns (bool hasDevice);
 
   // This method is used to propagate storage activities from the child actor
   // to the parent actor. See StorageActivityService.