Bug 1537899 - Add neck model capability for VRPose position. r=kip

Add neck model capability for VRPose position.

Differential Revision: https://phabricator.services.mozilla.com/D24386

--HG--
extra : moz-landing-system : lando

dom/vr/VRDisplay.cpp

@@ -246,7 +246,9 @@ void VRPose::GetPosition(JSContext* aCx, JS::MutableHandle<JSObject*> aRetval,
   SetFloat32Array(
       aCx, aRetval, mPosition, mVRState.pose.position, 3,
       !mPosition &&
-          bool(mVRState.flags & gfx::VRDisplayCapabilityFlags::Cap_Position),
+          (bool(mVRState.flags & gfx::VRDisplayCapabilityFlags::Cap_Position) ||
+           bool(mVRState.flags &
+                gfx::VRDisplayCapabilityFlags::Cap_PositionEmulated)),
       aRv);
 }
 

gfx/vr/external_api/moz_external_vr.h

@@ -34,7 +34,7 @@ enum class GamepadCapabilityFlags : uint16_t;
 #endif  //  MOZILLA_INTERNAL_API
 namespace gfx {
 
-static const int32_t kVRExternalVersion = 6;
+static const int32_t kVRExternalVersion = 7;
 
 // We assign VR presentations to groups with a bitmask.
 // Currently, we will only display either content or chrome.
@@ -159,10 +159,15 @@ enum class VRDisplayCapabilityFlags : uint16_t {
    * user is wearing the device.
    */
   Cap_MountDetection = 1 << 8,
+  /**
+   * Cap_PositionEmulated is set if the VRDisplay is capable of setting a
+   * emulated position (e.g. neck model) even if still doesn't support 6DOF tracking.
+   */
+  Cap_PositionEmulated = 1 << 9,
   /**
    * Cap_All used for validity checking during IPC serialization
    */
-  Cap_All = (1 << 9) - 1
+  Cap_All = (1 << 10) - 1
 };
 
 #ifdef MOZILLA_INTERNAL_API