DevTools: Change RemoteObject._describe method for Errors

LayoutTests/inspector/console/console-dir-expected.txt

Index: LayoutTests/inspector/console/console-dir-expected.txt
diff --git a/LayoutTests/inspector/console/console-dir-expected.txt b/LayoutTests/inspector/console/console-dir-expected.txt
index 5a051518df6caf478585efb10bdd191a35985aa7..c8746a296ecd1a93f5bfc45166e60619baa3a982 100644
--- a/LayoutTests/inspector/console/console-dir-expected.txt
+++ b/LayoutTests/inspector/console/console-dir-expected.txt
@@ -16,13 +16,13 @@ NodeList[1]
     length: 1
     __proto__: NodeList console-dir.html:10
 XPathResult
-    booleanValue: [Exception: TypeError]
+    booleanValue: [Exception: TypeError: Failed to read the 'booleanValue' property from 'XPathResult': The result type is not a boolean.]
     invalidIteratorState: false
-    numberValue: [Exception: TypeError]
+    numberValue: [Exception: TypeError: Failed to read the 'numberValue' property from 'XPathResult': The result type is not a number.]
     resultType: 4
-    singleNodeValue: [Exception: TypeError]
-    snapshotLength: [Exception: TypeError]
-    stringValue: [Exception: TypeError]
+    singleNodeValue: [Exception: TypeError: Failed to read the 'singleNodeValue' property from 'XPathResult': The result type is not a single node.]
+    snapshotLength: [Exception: TypeError: Failed to read the 'snapshotLength' property from 'XPathResult': The result type is not a snapshot.]
+    stringValue: [Exception: TypeError: Failed to read the 'stringValue' property from 'XPathResult': The result type is not a string.]
     __proto__: XPathResult console-dir.html:11
 Object
     "": ""