Bug 1577966 [wpt PR 18774] - Update interfaces/InputDeviceCapabilities.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/InputDeviceCapabilities.idl (#18774)

Source: https://github.com/tidoust/reffy-reports/blob/a1fde73/whatwg/idl/InputDeviceCapabilities.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/579102609
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wpt-commits: 00787d305e68711f5b20af310ab9bc508d6cb5ab
wpt-pr: 18774

testing/web-platform/tests/interfaces/InputDeviceCapabilities.idl

@@ -3,7 +3,8 @@
 // (https://github.com/tidoust/reffy-reports)
 // Source: Input Device Capabilities (https://wicg.github.io/InputDeviceCapabilities/)
 
-[Constructor(optional InputDeviceCapabilitiesInit deviceInitDict)]
+[Exposed=Window,
+ Constructor(optional InputDeviceCapabilitiesInit deviceInitDict = {})]
 interface InputDeviceCapabilities {
   readonly attribute boolean firesTouchEvents;
   readonly attribute boolean pointerMovementScrolls;