Propagate JSFailed error & conditionally execute initial assertion when converting error to JS value.

components/script/dom/bindings/error.rs

@@ -303,7 +303,10 @@ impl Error {
         global: &GlobalScope,
         rval: MutableHandleValue,
     ) {
-        assert!(!JS_IsExceptionPending(cx));
+        match self {
+            Error::JSFailed => (),
+            _ => assert!(!JS_IsExceptionPending(cx)),
+        }
         throw_dom_exception(cx, global, self);
         assert!(JS_IsExceptionPending(cx));
         assert!(JS_GetPendingException(cx, rval));

components/script/dom/permissions.rs

@@ -31,8 +31,6 @@ const DIALOG_TITLE: &'static str = "Permission request dialog";
 const NONSECURE_DIALOG_MESSAGE: &'static str = "feature is only safe to use in secure context,\
  but servo can't guarantee\n that the current context is secure. Do you want to proceed and grant permission?";
 const REQUEST_DIALOG_MESSAGE: &'static str = "Do you want to grant permission for";
-const ROOT_DESC_CONVERSION_ERROR: &'static str =
-    "Can't convert to an IDL value of type PermissionDescriptor";
 
 pub trait PermissionAlgorithm {
     type Descriptor;
@@ -237,7 +235,7 @@ impl PermissionAlgorithm for Permissions {
             match PermissionDescriptor::new(cx, property.handle()) {
                 Ok(ConversionResult::Success(descriptor)) => Ok(descriptor),
                 Ok(ConversionResult::Failure(error)) => Err(Error::Type(error.into_owned())),
-                Err(_) => Err(Error::Type(String::from(ROOT_DESC_CONVERSION_ERROR))),
+                Err(_) => Err(Error::JSFailed),
             }
         }
     }

tests/wpt/metadata/permissions/interfaces.any.js.ini

@@ -1,6 +1,10 @@
 [interfaces.any.html]
-  expected: CRASH
+  [Permissions interface: operation query(object)]
+    expected: FAIL
+
+  [Permissions interface: calling query(object) on navigator.permissions with too few arguments must throw TypeError]
+    expected: FAIL
+
 
 [interfaces.any.worker.html]
-  expected: CRASH
-
+  expected: CRASH

tests/wpt/metadata/permissions/test-background-fetch-permission.html.ini

@@ -1,5 +1,3 @@
 [test-background-fetch-permission.html]
-  expected: CRASH
   [Test Background Fetch Permission.]
-    expected: FAIL
-
+    expected: FAIL