DevTools: Change RemoteObject._describe method for Errors

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

 CONSOLE MESSAGE: line 9: test1,test2
 CONSOLE MESSAGE: line 10: [object NodeList]
 CONSOLE MESSAGE: line 11: [object XPathResult]
 CONSOLE MESSAGE: line 21: [object Object]
 CONSOLE MESSAGE: line 24: function () {}
 CONSOLE MESSAGE: line 28: [object Object]
 Tests that console logging dumps proper messages.
 
 Array[2]
     0: "test1"
     1: "test2"
     length: 2
     __proto__: Array[0] console-dir.html:9
 NodeList[1]
     0: html
     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
     "": ""
     "  ": "  "
     " a b ": " a b "
     $foo5_: 0
     "a↵↵b↵c": "a↵↵b↵c"
     c d: "c d"
     negZero: -0
     __proto__: Object console-dir.html:21
 function () {}
     arguments: null
     caller: null
     length: 0
     name: ""
     prototype: Object
     __proto__: function Empty() {}
     <function scope> console-dir.html:24
 outer.inner
     __proto__: outer.inner console-dir.html:28